| Message ID | 1342776046-25513-2-git-send-email-Joakim.Tjernlund@transmode.se |
|---|---|
| State | Superseded, archived |
| Headers | show |
On 07/20/2012 04:20 AM, Joakim Tjernlund wrote: > PowerPC mandates SP to be 16 bytes aligned. > Furthermore, a stack frame is added, pointing to the reset vector > which is just get in the way when gdb is walking the stack because > the reset vector may not accessible depending on emulator settings. > Also use a temp register so gdb doesn't pick up intermediate values. > > Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> > --- > arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- > 1 files changed, 5 insertions(+), 11 deletions(-) > > diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S > index 8d66cf1..8c75af9 100644 > --- arch/powerpc/cpu/mpc85xx/start.S > +++ arch/powerpc/cpu/mpc85xx/start.S > @@ -848,18 +848,12 @@ version_string: > .globl _start_cont > _start_cont: > /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ > - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h > - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l > - > + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h > + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ Please don't use r2 as a general purpose register -- even if it's early enough that we haven't started using it for its fixed purpose yet. > + stw r0,-4(r2) /* Store a NULL LR */ > + stw r0,0(r2) /* Store a NULL Back Chain */ > + mr r1,r2 /* Transfer to SP(r1) */ Why are you storing anything below the stack pointer? LR goes above the backchain, not below -- and it's not valid anyway for the current stack frame. If you want to have a terminating stack frame with a NULL LR, you need to create a second stack frame, like the code currently does. -Scott
Scott Wood <scottwood@freescale.com> wrote on 2012/07/20 23:11:33: > > On 07/20/2012 04:20 AM, Joakim Tjernlund wrote: > > PowerPC mandates SP to be 16 bytes aligned. > > Furthermore, a stack frame is added, pointing to the reset vector > > which is just get in the way when gdb is walking the stack because > > the reset vector may not accessible depending on emulator settings. > > Also use a temp register so gdb doesn't pick up intermediate values. > > > > Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> > > --- > > arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- > > 1 files changed, 5 insertions(+), 11 deletions(-) > > > > diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S > > index 8d66cf1..8c75af9 100644 > > --- arch/powerpc/cpu/mpc85xx/start.S > > +++ arch/powerpc/cpu/mpc85xx/start.S > > @@ -848,18 +848,12 @@ version_string: > > .globl _start_cont > > _start_cont: > > /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ > > - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h > > - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l > > - > > + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h > > + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > > Please don't use r2 as a general purpose register -- even if it's early > enough that we haven't started using it for its fixed purpose yet. I guess that would be a tiny improvement, but it is nothing compared with the r1 abuse in this file :) > > > + stw r0,-4(r2) /* Store a NULL LR */ > > + stw r0,0(r2) /* Store a NULL Back Chain */ > > + mr r1,r2 /* Transfer to SP(r1) */ > > Why are you storing anything below the stack pointer? LR goes above the > backchain, not below -- and it's not valid anyway for the current stack > frame. If you want to have a terminating stack frame with a NULL LR, > you need to create a second stack frame, like the code currently does. Right, it should be +4 where the NULL LR should be. As you said, it doesn't matter because it is not valid for this stack frame and could be left out. I do not want to create a frame as the current code does, it might create an memory access to 0xfffffffc which I don't want. How about this then: lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ li r0,0 stw r0,0(r3) /* Terminate Back Chain */ stw r0,+4(r3) /* NULL LR, to be nice. */ mr r1,r3 /* Transfer to SP(r1) */ or if that reset address is wanted: lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ li r0,0 stw r0,0(r3) /* Terminate Back Chain */ stw r0,+4(r3) /* NULL LR, to be nice. */ stwu r3,-16(r3) /* save back chain and move SP */ lis r0,RESET_VECTOR@h ori r0,RESET_VECTOR@l stw r0,+20(r3) /* save return address */ mr r1,r3 /* Transfer to SP(r1) */ I would have to test with the emulator if both are OK or if there will be an access to RESET_VECTOR(I don't have that connected ATM). Jocke
> > > Scott Wood <scottwood@freescale.com> wrote on 2012/07/20 23:11:33: > > > > On 07/20/2012 04:20 AM, Joakim Tjernlund wrote: > > > PowerPC mandates SP to be 16 bytes aligned. > > > Furthermore, a stack frame is added, pointing to the reset vector > > > which is just get in the way when gdb is walking the stack because > > > the reset vector may not accessible depending on emulator settings. > > > Also use a temp register so gdb doesn't pick up intermediate values. > > > > > > Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> > > > --- > > > arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- > > > 1 files changed, 5 insertions(+), 11 deletions(-) > > > > > > diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S > > > index 8d66cf1..8c75af9 100644 > > > --- arch/powerpc/cpu/mpc85xx/start.S > > > +++ arch/powerpc/cpu/mpc85xx/start.S > > > @@ -848,18 +848,12 @@ version_string: > > > .globl _start_cont > > > _start_cont: > > > /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ > > > - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h > > > - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l > > > - > > > + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h > > > + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > > > > Please don't use r2 as a general purpose register -- even if it's early > > enough that we haven't started using it for its fixed purpose yet. > > I guess that would be a tiny improvement, but it is nothing compared > with the r1 abuse in this file :) > > > > > > + stw r0,-4(r2) /* Store a NULL LR */ > > > + stw r0,0(r2) /* Store a NULL Back Chain */ > > > + mr r1,r2 /* Transfer to SP(r1) */ > > > > Why are you storing anything below the stack pointer? LR goes above the > > backchain, not below -- and it's not valid anyway for the current stack > > frame. If you want to have a terminating stack frame with a NULL LR, > > you need to create a second stack frame, like the code currently does. > > Right, it should be +4 where the NULL LR should be. As you said, it doesn't matter > because it is not valid for this stack frame and could be left out. > > I do not want to create a frame as the current code does, it > might create an memory access to 0xfffffffc which I don't want. > How about this then: > > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > li r0,0 > stw r0,0(r3) /* Terminate Back Chain */ > stw r0,+4(r3) /* NULL LR, to be nice. */ > mr r1,r3 /* Transfer to SP(r1) */ > > or if that reset address is wanted: > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > li r0,0 > stw r0,0(r3) /* Terminate Back Chain */ > stw r0,+4(r3) /* NULL LR, to be nice. */ > stwu r3,-16(r3) /* save back chain and move SP */ > lis r0,RESET_VECTOR@h > ori r0,RESET_VECTOR@l > stw r0,+20(r3) /* save return address */ > mr r1,r3 /* Transfer to SP(r1) */ > > I would have to test with the emulator if both are OK or if there will > be an access to RESET_VECTOR(I don't have that connected ATM). So I got the BDI connected and did som experiments. Having RESET_VECTOR in the initial stack chain makes gdb print this: (gdb) bt #0 cpu_init_early_f () at cpu_init_early.c:116 #1 0xeff800a4 in _start_cont () at start.S:877 Backtrace stopped: frame did not save the PC (gdb) So I don't think there is any benefit trying to squeeze RESET_VECTOR into the stack chain. Jocke
On 07/21/2012 10:06 AM, Joakim Tjernlund wrote: > > Scott Wood <scottwood@freescale.com> wrote on 2012/07/20 23:11:33: >> >> On 07/20/2012 04:20 AM, Joakim Tjernlund wrote: >>> PowerPC mandates SP to be 16 bytes aligned. >>> Furthermore, a stack frame is added, pointing to the reset vector >>> which is just get in the way when gdb is walking the stack because >>> the reset vector may not accessible depending on emulator settings. >>> Also use a temp register so gdb doesn't pick up intermediate values. >>> >>> Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> >>> --- >>> arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- >>> 1 files changed, 5 insertions(+), 11 deletions(-) >>> >>> diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S >>> index 8d66cf1..8c75af9 100644 >>> --- arch/powerpc/cpu/mpc85xx/start.S >>> +++ arch/powerpc/cpu/mpc85xx/start.S >>> @@ -848,18 +848,12 @@ version_string: >>> .globl _start_cont >>> _start_cont: >>> /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ >>> - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h >>> - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l >>> - >>> + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h >>> + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ >> >> Please don't use r2 as a general purpose register -- even if it's early >> enough that we haven't started using it for its fixed purpose yet. > > I guess that would be a tiny improvement, but it is nothing compared > with the r1 abuse in this file :) Yeah, I just wanted to discourage making it worse. >>> + stw r0,-4(r2) /* Store a NULL LR */ >>> + stw r0,0(r2) /* Store a NULL Back Chain */ >>> + mr r1,r2 /* Transfer to SP(r1) */ >> >> Why are you storing anything below the stack pointer? LR goes above the >> backchain, not below -- and it's not valid anyway for the current stack >> frame. If you want to have a terminating stack frame with a NULL LR, >> you need to create a second stack frame, like the code currently does. > > Right, it should be +4 where the NULL LR should be. As you said, it doesn't matter > because it is not valid for this stack frame and could be left out. > > I do not want to create a frame as the current code does, it > might create an memory access to 0xfffffffc which I don't want. How would that happen? > How about this then: > > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > li r0,0 > stw r0,0(r3) /* Terminate Back Chain */ > stw r0,+4(r3) /* NULL LR, to be nice. */ > mr r1,r3 /* Transfer to SP(r1) */ > > or if that reset address is wanted: > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > li r0,0 > stw r0,0(r3) /* Terminate Back Chain */ > stw r0,+4(r3) /* NULL LR, to be nice. */ > stwu r3,-16(r3) /* save back chain and move SP */ > lis r0,RESET_VECTOR@h > ori r0,RESET_VECTOR@l > stw r0,+20(r3) /* save return address */ > mr r1,r3 /* Transfer to SP(r1) */ > > I would have to test with the emulator if both are OK or if there will > be an access to RESET_VECTOR(I don't have that connected ATM). How about: lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ li r0,0 stw r0,0(r3) /* Terminate Back Chain */ stw r0,4(r3) /* NULL LR, to be nice. */ stwu r3,-16(r3) /* Create new stack frame * so NULL LR is valid */ mr r1,r3 /* Transfer to SP(r1) */ -Scott
Scott Wood <scottwood@freescale.com> wrote on 2012/07/23 18:52:28: > From: Scott Wood <scottwood@freescale.com> > To: Joakim Tjernlund <joakim.tjernlund@transmode.se>, > Cc: <u-boot@lists.denx.de> > Date: 2012/07/23 18:52 > Subject: Re: [U-Boot] [PATCH 2/2] mpc85xx: Initial SP alignment is wrong. > > On 07/21/2012 10:06 AM, Joakim Tjernlund wrote: > > > > Scott Wood <scottwood@freescale.com> wrote on 2012/07/20 23:11:33: > >> > >> On 07/20/2012 04:20 AM, Joakim Tjernlund wrote: > >>> PowerPC mandates SP to be 16 bytes aligned. > >>> Furthermore, a stack frame is added, pointing to the reset vector > >>> which is just get in the way when gdb is walking the stack because > >>> the reset vector may not accessible depending on emulator settings. > >>> Also use a temp register so gdb doesn't pick up intermediate values. > >>> > >>> Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> > >>> --- > >>> arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- > >>> 1 files changed, 5 insertions(+), 11 deletions(-) > >>> > >>> diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S > >>> index 8d66cf1..8c75af9 100644 > >>> --- arch/powerpc/cpu/mpc85xx/start.S > >>> +++ arch/powerpc/cpu/mpc85xx/start.S > >>> @@ -848,18 +848,12 @@ version_string: > >>> .globl _start_cont > >>> _start_cont: > >>> /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ > >>> - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h > >>> - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l > >>> - > >>> + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h > >>> + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > >> > >> Please don't use r2 as a general purpose register -- even if it's early > >> enough that we haven't started using it for its fixed purpose yet. > > > > I guess that would be a tiny improvement, but it is nothing compared > > with the r1 abuse in this file :) > > Yeah, I just wanted to discourage making it worse. > > >>> + stw r0,-4(r2) /* Store a NULL LR */ > >>> + stw r0,0(r2) /* Store a NULL Back Chain */ > >>> + mr r1,r2 /* Transfer to SP(r1) */ > >> > >> Why are you storing anything below the stack pointer? LR goes above the > >> backchain, not below -- and it's not valid anyway for the current stack > >> frame. If you want to have a terminating stack frame with a NULL LR, > >> you need to create a second stack frame, like the code currently does. > > > > Right, it should be +4 where the NULL LR should be. As you said, it doesn't matter > > because it is not valid for this stack frame and could be left out. > > > > I do not want to create a frame as the current code does, it > > might create an memory access to 0xfffffffc which I don't want. > > How would that happen? > > > How about this then: > > > > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > > li r0,0 > > stw r0,0(r3) /* Terminate Back Chain */ > > stw r0,+4(r3) /* NULL LR, to be nice. */ > > mr r1,r3 /* Transfer to SP(r1) */ > > > > or if that reset address is wanted: > > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > > li r0,0 > > stw r0,0(r3) /* Terminate Back Chain */ > > stw r0,+4(r3) /* NULL LR, to be nice. */ > > stwu r3,-16(r3) /* save back chain and move SP */ > > lis r0,RESET_VECTOR@h > > ori r0,RESET_VECTOR@l > > stw r0,+20(r3) /* save return address */ > > mr r1,r3 /* Transfer to SP(r1) */ > > > > I would have to test with the emulator if both are OK or if there will > > be an access to RESET_VECTOR(I don't have that connected ATM). > > How about: > > lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h > ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ > li r0,0 > stw r0,0(r3) /* Terminate Back Chain */ > stw r0,4(r3) /* NULL LR, to be nice. */ > stwu r3,-16(r3) /* Create new stack frame > * so NULL LR is valid > */ > mr r1,r3 /* Transfer to SP(r1) */ This also confuses gdb (gdb) bt #0 cpu_init_early_f () at cpu_init_early.c:96 #1 0xeff80098 in _start_cont () at start.S:863 Backtrace stopped: frame did not save the PC that extra stwu creates an improper call chain. We have the initial stack frame already without the stwu Jocke
On 07/23/2012 12:11 PM, Joakim Tjernlund wrote: > > > Scott Wood <scottwood@freescale.com> wrote on 2012/07/23 18:52:28: > >> From: Scott Wood <scottwood@freescale.com> >> To: Joakim Tjernlund <joakim.tjernlund@transmode.se>, >> Cc: <u-boot@lists.denx.de> >> Date: 2012/07/23 18:52 >> Subject: Re: [U-Boot] [PATCH 2/2] mpc85xx: Initial SP alignment is wrong. >> >> On 07/21/2012 10:06 AM, Joakim Tjernlund wrote: >>> >>> Scott Wood <scottwood@freescale.com> wrote on 2012/07/20 23:11:33: >>>> >>>> On 07/20/2012 04:20 AM, Joakim Tjernlund wrote: >>>>> PowerPC mandates SP to be 16 bytes aligned. >>>>> Furthermore, a stack frame is added, pointing to the reset vector >>>>> which is just get in the way when gdb is walking the stack because >>>>> the reset vector may not accessible depending on emulator settings. >>>>> Also use a temp register so gdb doesn't pick up intermediate values. >>>>> >>>>> Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> >>>>> --- >>>>> arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- >>>>> 1 files changed, 5 insertions(+), 11 deletions(-) >>>>> >>>>> diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S >>>>> index 8d66cf1..8c75af9 100644 >>>>> --- arch/powerpc/cpu/mpc85xx/start.S >>>>> +++ arch/powerpc/cpu/mpc85xx/start.S >>>>> @@ -848,18 +848,12 @@ version_string: >>>>> .globl _start_cont >>>>> _start_cont: >>>>> /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ >>>>> - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h >>>>> - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l >>>>> - >>>>> + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h >>>>> + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ >>>> >>>> Please don't use r2 as a general purpose register -- even if it's early >>>> enough that we haven't started using it for its fixed purpose yet. >>> >>> I guess that would be a tiny improvement, but it is nothing compared >>> with the r1 abuse in this file :) >> >> Yeah, I just wanted to discourage making it worse. >> >>>>> + stw r0,-4(r2) /* Store a NULL LR */ >>>>> + stw r0,0(r2) /* Store a NULL Back Chain */ >>>>> + mr r1,r2 /* Transfer to SP(r1) */ >>>> >>>> Why are you storing anything below the stack pointer? LR goes above the >>>> backchain, not below -- and it's not valid anyway for the current stack >>>> frame. If you want to have a terminating stack frame with a NULL LR, >>>> you need to create a second stack frame, like the code currently does. >>> >>> Right, it should be +4 where the NULL LR should be. As you said, it doesn't matter >>> because it is not valid for this stack frame and could be left out. >>> >>> I do not want to create a frame as the current code does, it >>> might create an memory access to 0xfffffffc which I don't want. >> >> How would that happen? >> >>> How about this then: >>> >>> lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h >>> ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ >>> li r0,0 >>> stw r0,0(r3) /* Terminate Back Chain */ >>> stw r0,+4(r3) /* NULL LR, to be nice. */ >>> mr r1,r3 /* Transfer to SP(r1) */ >>> >>> or if that reset address is wanted: >>> lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h >>> ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ >>> li r0,0 >>> stw r0,0(r3) /* Terminate Back Chain */ >>> stw r0,+4(r3) /* NULL LR, to be nice. */ >>> stwu r3,-16(r3) /* save back chain and move SP */ >>> lis r0,RESET_VECTOR@h >>> ori r0,RESET_VECTOR@l >>> stw r0,+20(r3) /* save return address */ >>> mr r1,r3 /* Transfer to SP(r1) */ >>> >>> I would have to test with the emulator if both are OK or if there will >>> be an access to RESET_VECTOR(I don't have that connected ATM). >> >> How about: >> >> lis r3,(CONFIG_SYS_INIT_RAM_ADDR)@h >> ori r3,r3,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ >> li r0,0 >> stw r0,0(r3) /* Terminate Back Chain */ >> stw r0,4(r3) /* NULL LR, to be nice. */ >> stwu r3,-16(r3) /* Create new stack frame >> * so NULL LR is valid >> */ >> mr r1,r3 /* Transfer to SP(r1) */ > > This also confuses gdb > (gdb) bt > #0 cpu_init_early_f () at cpu_init_early.c:96 > #1 0xeff80098 in _start_cont () at start.S:863 > Backtrace stopped: frame did not save the PC > > that extra stwu creates an improper call chain. > We have the initial stack frame already without the stwu Well, we do want it to stop the backtrace at that point. :-) ...but I was a bit confused when I thought it would help terminate things. The NULL LR only helps prevent finding something worse, if something happens to do a backtrace immediately after the first stwu but before a real LR is saved. -Scott
Scott Wood <scottwood@freescale.com> wrote on 2012/07/23 19:28:20: > > On 07/23/2012 12:11 PM, Joakim Tjernlund wrote: > > > > > ...but I was a bit confused when I thought it would help terminate > things. The NULL LR only helps prevent finding something worse, if > something happens to do a backtrace immediately after the first stwu but > before a real LR is saved. So I just sent v2, now I am offline for a few days/a week. Jocke
diff --git arch/powerpc/cpu/mpc85xx/start.S arch/powerpc/cpu/mpc85xx/start.S index 8d66cf1..8c75af9 100644 --- arch/powerpc/cpu/mpc85xx/start.S +++ arch/powerpc/cpu/mpc85xx/start.S @@ -848,18 +848,12 @@ version_string: .globl _start_cont _start_cont: /* Setup the stack in initial RAM,could be L2-as-SRAM or L1 dcache*/ - lis r1,CONFIG_SYS_INIT_RAM_ADDR@h - ori r1,r1,CONFIG_SYS_INIT_SP_OFFSET@l - + lis r2,(CONFIG_SYS_INIT_RAM_ADDR)@h + ori r2,r2,((CONFIG_SYS_INIT_SP_OFFSET-16)&~0xf)@l /* Align to 16 */ li r0,0 - stwu r0,-4(r1) - stwu r0,-4(r1) /* Terminate call chain */ - - stwu r1,-8(r1) /* Save back chain and move SP */ - lis r0,RESET_VECTOR@h /* Address of reset vector */ - ori r0,r0,RESET_VECTOR@l - stwu r1,-8(r1) /* Save back chain and move SP */ - stw r0,+12(r1) /* Save return addr (underflow vect) */ + stw r0,-4(r2) /* Store a NULL LR */ + stw r0,0(r2) /* Store a NULL Back Chain */ + mr r1,r2 /* Transfer to SP(r1) */ GET_GOT bl cpu_init_early_f
PowerPC mandates SP to be 16 bytes aligned. Furthermore, a stack frame is added, pointing to the reset vector which is just get in the way when gdb is walking the stack because the reset vector may not accessible depending on emulator settings. Also use a temp register so gdb doesn't pick up intermediate values. Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se> --- arch/powerpc/cpu/mpc85xx/start.S | 16 +++++----------- 1 files changed, 5 insertions(+), 11 deletions(-)