Richard Biener <richard.guent...@gmail.com> writes: > On Fri, Apr 11, 2025 at 11:10 AM Richard Sandiford > <richard.sandif...@arm.com> wrote: >> >> Richard Biener <richard.guent...@gmail.com> writes: >> > On Thu, Apr 10, 2025 at 10:10 PM Richard Sandiford >> > <richard.sandif...@arm.com> wrote: >> >> >> >> PR119610 is about incorrect CFI output for a stack probe when that >> >> probe is not the initial allocation. The main aarch64 stack probe >> >> function, aarch64_allocate_and_probe_stack_space, implicitly assumed >> >> that the incoming stack pointer pointed to the top of the frame, >> >> and thus held the CFA. >> >> >> >> aarch64_save_callee_saves and aarch64_restore_callee_saves use a >> >> parameter called bytes_below_sp to track how far the stack pointer >> >> is above the base of the static frame. This patch does the same >> >> thing for aarch64_allocate_and_probe_stack_space. >> >> >> >> Also, I noticed that the SVE path was attaching the first CFA note >> >> to the wrong instruction: it was attaching the note to the calculation >> >> of the stack size, rather than to the r11<-sp copy. >> >> >> >> Bootstrapped & regression-tested on aarch64-linux-gnu. I'll push on >> >> Monday if there are no comments before then. I'd appreciate a second >> >> pair of eyes though, since this is a sensitive area. >> > >> > Do you happen to know if the backports to older branches you provided for >> > the change that triggered this issue (in particular to GCC 7) are also >> > affected? >> >> GCC 7 and GCC 8 should be ok. The bug relies on stack protection being >> enabled (-fstack-protector-strong for the testcase in the PR, but just >> -fstack-protector for others) and that was added in GCC 9. > > Hmm, I see -fstack-protector[-strong] working with GCC 7 on aarch64.
I think it's just being silently accepted as a nop. At least: > Specifically > the testcase produces for foo(): > > .text > .align 2 > .global _Z3foov > .type _Z3foov, %function > _Z3foov: > .LFB0: > .cfi_startproc > stp x29, x30, [sp, -16]! > .cfi_def_cfa_offset 16 > .cfi_offset 29, -16 > .cfi_offset 30, -8 > add x29, sp, 0 > .cfi_def_cfa_register 29 > sub sp, sp, #16 > sub sp, sp, #524288 ...the function isn't probing the stack here. It ought to be doing something like the code that Alex quoted in the PR. Compare the GCC 8 and GCC 9 output in https://godbolt.org/z/cWbsG3eGb . Thanks, Richard > adrp x0, __stack_chk_guard > add x0, x0, :lo12:__stack_chk_guard > ldr x1, [x0] > str x1, [x29, -8] > mov x1,0 > adrp x0, ptr > add x0, x0, :lo12:ptr > sub x1, x29, #524288 > sub x1, x1, #8 > str x1, [x0] > mov x0, 4 > bl __cxa_allocate_exception > mov x3, x0 > mov w0, 1 > str w0, [x3] > adrp x0, _ZTIi > add x0, x0, :lo12:_ZTIi > mov x2, 0 > mov x1, x0 > mov x0, x3 > bl __cxa_throw > .cfi_endproc > .LFE0: > .size _Z3foov, .-_Z3foov
