| Message ID | orfs04324k.fsf@lxoliva.fsfla.org |
|---|---|
| State | New |
| Headers | show |
| Series | [#1/2] strub: sparc: omit frame in strub_leave [PR112917] | expand |
On Thu, Dec 14, 2023 at 10:29 PM Alexandre Oliva <oliva@adacore.com> wrote: > > > The stack pointer is biased by 2047 bytes on sparc64, so the range it > delimits is way off. Unbias the addresses returned by > __builtin_stack_address (), so that the strub builtins, inlined or > not, can function correctly. I've considered introducing a new target > macro, but using STACK_POINTER_OFFSET seems safe, and it enables the > register save areas to be scrubbed as well. > > Because of the large fixed-size outgoing args area next to the > register save area on sparc, we still need __strub_leave to not > allocate its own frame, otherwise it won't be able to clear part of > the frame it should. > > Regstrapped on x86_64-linux-gnu, also testing on sparc-solaris2.11.3. > Ok to install? It might be worth amending the documentation in case this is unexpected to users? > > > for gcc/ChangeLog > > PR middle-end/112917 > * builtins.cc (expand_bultin_stack_address): Add > STACK_POINTER_OFFSET. > --- > gcc/builtins.cc | 34 ++++++++++++++++++++++++++++++++-- > 1 file changed, 32 insertions(+), 2 deletions(-) > > diff --git a/gcc/builtins.cc b/gcc/builtins.cc > index 7c2732ab79e6f..4c8c514fe8618 100644 > --- a/gcc/builtins.cc > +++ b/gcc/builtins.cc > @@ -5443,8 +5443,38 @@ expand_builtin_frame_address (tree fndecl, tree exp) > static rtx > expand_builtin_stack_address () > { > - return convert_to_mode (ptr_mode, copy_to_reg (stack_pointer_rtx), > - STACK_UNSIGNED); > + rtx ret = convert_to_mode (ptr_mode, copy_to_reg (stack_pointer_rtx), > + STACK_UNSIGNED); > + > + /* Unbias the stack pointer, bringing it to the boundary between the > + stack area claimed by the active function calling this builtin, > + and stack ranges that could get clobbered if it called another > + function. It should NOT encompass any stack red zone, that is > + used in leaf functions. > + > + On SPARC, the register save area is *not* considered active or > + used by the active function, but rather as akin to the area in > + which call-preserved registers are saved by callees. This > + enables __strub_leave to clear what would otherwise overlap with > + its own register save area. > + > + If the address is computed too high or too low, parts of a stack > + range that should be scrubbed may be left unscrubbed, scrubbing > + may corrupt active portions of the stack frame, and stack ranges > + may be doubly-scrubbed by caller and callee. > + > + In order for it to be just right, the area delimited by > + @code{__builtin_stack_address} and @code{__builtin_frame_address > + (0)} should encompass caller's registers saved by the function, > + local on-stack variables and @code{alloca} stack areas. > + Accumulated outgoing on-stack arguments, preallocated as part of > + a function's own prologue, are to be regarded as part of the > + (caller) function's active area as well, whereas those pushed or > + allocated temporarily for a call are regarded as part of the > + callee's stack range, rather than the caller's. */ > + ret = plus_constant (ptr_mode, ret, STACK_POINTER_OFFSET); > + > + return force_reg (ptr_mode, ret); > } > > /* Expand a call to builtin function __builtin_strub_enter. */ > > -- > Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ > Free Software Activist GNU Toolchain Engineer > More tolerance and less prejudice are key for inclusion and diversity > Excluding neuro-others for not behaving ""normal"" is *not* inclusive
diff --git a/gcc/builtins.cc b/gcc/builtins.cc index 7c2732ab79e6f..4c8c514fe8618 100644 --- a/gcc/builtins.cc +++ b/gcc/builtins.cc @@ -5443,8 +5443,38 @@ expand_builtin_frame_address (tree fndecl, tree exp) static rtx expand_builtin_stack_address () { - return convert_to_mode (ptr_mode, copy_to_reg (stack_pointer_rtx), - STACK_UNSIGNED); + rtx ret = convert_to_mode (ptr_mode, copy_to_reg (stack_pointer_rtx), + STACK_UNSIGNED); + + /* Unbias the stack pointer, bringing it to the boundary between the + stack area claimed by the active function calling this builtin, + and stack ranges that could get clobbered if it called another + function. It should NOT encompass any stack red zone, that is + used in leaf functions. + + On SPARC, the register save area is *not* considered active or + used by the active function, but rather as akin to the area in + which call-preserved registers are saved by callees. This + enables __strub_leave to clear what would otherwise overlap with + its own register save area. + + If the address is computed too high or too low, parts of a stack + range that should be scrubbed may be left unscrubbed, scrubbing + may corrupt active portions of the stack frame, and stack ranges + may be doubly-scrubbed by caller and callee. + + In order for it to be just right, the area delimited by + @code{__builtin_stack_address} and @code{__builtin_frame_address + (0)} should encompass caller's registers saved by the function, + local on-stack variables and @code{alloca} stack areas. + Accumulated outgoing on-stack arguments, preallocated as part of + a function's own prologue, are to be regarded as part of the + (caller) function's active area as well, whereas those pushed or + allocated temporarily for a call are regarded as part of the + callee's stack range, rather than the caller's. */ + ret = plus_constant (ptr_mode, ret, STACK_POINTER_OFFSET); + + return force_reg (ptr_mode, ret); } /* Expand a call to builtin function __builtin_strub_enter. */