Message ID | 20220825210103.2259134-1-richard.henderson@linaro.org |
---|---|
State | New |
Headers | show |
Series | [RESEND] Makeconfig: Set pie-ccflag to -fPIE by default | expand |
On 25/08/22 18:01, Richard Henderson via Libc-alpha wrote: > [ I never saw this arrive in the list archives. > Trying again with my linaro address subscribed. ] > > We should default to the larger code model, in order to support > larger applications built with -static -pie. This should be > consistent with pic-ccflag, which defaults to -fPIC. > > Remove the now redundant override from sysdeps/sparc/Makefile. > Note that -fno-pie and -fno-PIE have the same effect. > > --- > > In the case of AArch64, the code changes are small but significant: > > 0000000000000000 <__libc_init_first>: > 0: a9bd7bfd stp x29, x30, [sp, #-48]! > - 4: 90000003 adrp x3, 0 <_GLOBAL_OFFSET_TABLE_> > - 4: R_AARCH64_ADR_PREL_PG_HI21 _GLOBAL_OFFSET_TABLE_ > + 4: 90000003 adrp x3, 0 <__environ> > + 4: R_AARCH64_ADR_GOT_PAGE __environ > 8: 90000004 adrp x4, 0 <__libc_init_first> > 8: R_AARCH64_ADR_PREL_PG_HI21 .bss > c: 910003fd mov x29, sp > 10: f9400063 ldr x3, [x3] > - 10: R_AARCH64_LD64_GOTPAGE_LO15 __environ > + 10: R_AARCH64_LD64_GOT_LO12_NC __environ > > In the small model, we are constrained to 15 bits of GOT, with a > single shared base, _GLOBAL_OFFSET_TABLE_. In the large model, > each symbol has a page + offset pair. For small functions like > this, where there are no other variable references to share the > common GOT pointer, there is no actual code change. > > r~ I recall that powerpc wanted to use -mcmodel=large, but it would require to adjust a lot of assembly implementations. Are we sure this change does not trigger any regression with current glibc code? > --- > Makeconfig | 2 +- > sysdeps/sparc/Makefile | 3 --- > 2 files changed, 1 insertion(+), 4 deletions(-) > > diff --git a/Makeconfig b/Makeconfig > index e78cf220af..f8164a0025 100644 > --- a/Makeconfig > +++ b/Makeconfig > @@ -1052,7 +1052,7 @@ pic-ccflag = -fPIC > PIC-ccflag = -fPIC > endif > # This can be changed by a sysdep makefile > -pie-ccflag = -fpie > +pie-ccflag = -fPIE > no-pie-ccflag = -fno-pie > # This one should always stay like this unless there is a very good reason. > PIE-ccflag = -fPIE > diff --git a/sysdeps/sparc/Makefile b/sysdeps/sparc/Makefile > index 12c2c1b085..26b4a84606 100644 > --- a/sysdeps/sparc/Makefile > +++ b/sysdeps/sparc/Makefile > @@ -1,9 +1,6 @@ > # The Sparc `long double' is a distinct type we support. > long-double-fcts = yes > > -pie-ccflag = -fPIE > -no-pie-ccflag = -fno-PIE > - > ifeq ($(subdir),gmon) > sysdep_routines += sparc-mcount > endif
On 8/26/22 05:32, Adhemerval Zanella Netto wrote: > > > On 25/08/22 18:01, Richard Henderson via Libc-alpha wrote: >> [ I never saw this arrive in the list archives. >> Trying again with my linaro address subscribed. ] >> >> We should default to the larger code model, in order to support >> larger applications built with -static -pie. This should be >> consistent with pic-ccflag, which defaults to -fPIC. >> >> Remove the now redundant override from sysdeps/sparc/Makefile. >> Note that -fno-pie and -fno-PIE have the same effect. >> >> --- >> >> In the case of AArch64, the code changes are small but significant: >> >> 0000000000000000 <__libc_init_first>: >> 0: a9bd7bfd stp x29, x30, [sp, #-48]! >> - 4: 90000003 adrp x3, 0 <_GLOBAL_OFFSET_TABLE_> >> - 4: R_AARCH64_ADR_PREL_PG_HI21 _GLOBAL_OFFSET_TABLE_ >> + 4: 90000003 adrp x3, 0 <__environ> >> + 4: R_AARCH64_ADR_GOT_PAGE __environ >> 8: 90000004 adrp x4, 0 <__libc_init_first> >> 8: R_AARCH64_ADR_PREL_PG_HI21 .bss >> c: 910003fd mov x29, sp >> 10: f9400063 ldr x3, [x3] >> - 10: R_AARCH64_LD64_GOTPAGE_LO15 __environ >> + 10: R_AARCH64_LD64_GOT_LO12_NC __environ >> >> In the small model, we are constrained to 15 bits of GOT, with a >> single shared base, _GLOBAL_OFFSET_TABLE_. In the large model, >> each symbol has a page + offset pair. For small functions like >> this, where there are no other variable references to share the >> common GOT pointer, there is no actual code change. >> >> r~ > > I recall that powerpc wanted to use -mcmodel=large, but it would require to > adjust a lot of assembly implementations. Are we sure this change does not > trigger any regression with current glibc code? Ah, the resend is missing some detail I included in the original: > For s390x, I would expect changes similar to c64a10e54441, and > an eventual similar bug report if this were left unchanged. > > For x86, ppc64 and riscv64, -fpie & -fPIE are identical. For ppc64 specifically, I audited gcc/config/rs6000/ for references to flag_pic, and the only changes between -fpic and -fPIC are for 32-bit ABI_V4. More generally, our assembly is already set up for -fPIC, which is the pic-ccflag default; the difference for -fPIE is only in the selection of external vs local binding. For aarch64, I've audited uses of the adrp instruction in sysdeps/, and they are what I'd expect, e.g. aarch64/start.S: adrp x0, :got:main and there are no instances of '_GLOBAL_OFFSET_TABLE_', which is indicative of -fpic. For s390, I've similarly audited uses of the larl instruction: s390/s390-64/start.S: larl %r2,main@GOTENT # load pointer to main r~
diff --git a/Makeconfig b/Makeconfig index e78cf220af..f8164a0025 100644 --- a/Makeconfig +++ b/Makeconfig @@ -1052,7 +1052,7 @@ pic-ccflag = -fPIC PIC-ccflag = -fPIC endif # This can be changed by a sysdep makefile -pie-ccflag = -fpie +pie-ccflag = -fPIE no-pie-ccflag = -fno-pie # This one should always stay like this unless there is a very good reason. PIE-ccflag = -fPIE diff --git a/sysdeps/sparc/Makefile b/sysdeps/sparc/Makefile index 12c2c1b085..26b4a84606 100644 --- a/sysdeps/sparc/Makefile +++ b/sysdeps/sparc/Makefile @@ -1,9 +1,6 @@ # The Sparc `long double' is a distinct type we support. long-double-fcts = yes -pie-ccflag = -fPIE -no-pie-ccflag = -fno-PIE - ifeq ($(subdir),gmon) sysdep_routines += sparc-mcount endif