llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-libunwind Author: John Brawn (john-brawn-arm) <details> <summary>Changes</summary> The libunwind assembly files need adjustment in order to work correctly when both BTI and GCS are both enabled (which will be the case when using -mbranch-protection=standard): * __libunwind_Registers_arm64_jumpto can't use br to jump to the return location, instead we need to use gcspush then ret. * Because we indirectly call __libunwind_Registers_arm64_jumpto it needs to start with bti jc. * We need to set the GCS GNU property bit when it's enabled. --- Full diff: https://github.com/llvm/llvm-project/pull/102322.diff 2 Files Affected: - (modified) libunwind/src/UnwindRegistersRestore.S (+15-1) - (modified) libunwind/src/assembly.h (+20-5) ``````````diff diff --git a/libunwind/src/UnwindRegistersRestore.S b/libunwind/src/UnwindRegistersRestore.S index b407221ca45f8..7783c94088f68 100644 --- a/libunwind/src/UnwindRegistersRestore.S +++ b/libunwind/src/UnwindRegistersRestore.S @@ -629,6 +629,10 @@ Lnovec: #elif defined(__aarch64__) +#if defined(__ARM_FEATURE_GCS_DEFAULT) +.arch_extension gcs +#endif + // // extern "C" void __libunwind_Registers_arm64_jumpto(Registers_arm64 *); // @@ -680,7 +684,17 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_arm64_jumpto) ldr x16, [x0, #0x0F8] ldp x0, x1, [x0, #0x000] // restore x0,x1 mov sp,x16 // restore sp - br x30 // jump to pc +#if defined(__ARM_FEATURE_GCS_DEFAULT) + // If GCS is enabled we need to push the address we're returning to onto the + // GCS stack. We can't just return using br, as there won't be a BTI landing + // pad instruction at the destination. + mov x16, #1 + chkfeat x16 + cbnz x16, Lnogcs + gcspushm x30 +Lnogcs: +#endif + ret // jump to pc #elif defined(__arm__) && !defined(__APPLE__) diff --git a/libunwind/src/assembly.h b/libunwind/src/assembly.h index fb07d04071af3..f8e83e138eff5 100644 --- a/libunwind/src/assembly.h +++ b/libunwind/src/assembly.h @@ -82,7 +82,22 @@ #define PPC64_OPD2 #endif -#if defined(__aarch64__) && defined(__ARM_FEATURE_BTI_DEFAULT) +#if defined(__aarch64__) +#if defined(__ARM_FEATURE_GCS_DEFAULT) && defined(__ARM_FEATURE_BTI_DEFAULT) +// Set BTI, PAC, and GCS gnu property bits +#define GNU_PROPERTY 7 +// We indirectly branch to __libunwind_Registers_arm64_jumpto from +// __unw_phase2_resume, so we need to use bti jc. +#define AARCH64_BTI bti jc +#elif defined(__ARM_FEATURE_GCS_DEFAULT) +// Set GCS gnu property bit +#define GNU_PROPERTY 4 +#elif defined(__ARM_FEATURE_BTI_DEFAULT) +// Set BTI and PAC gnu property bits +#define GNU_PROPERTY 3 +#define AARCH64_BTI bti c +#endif +#ifdef GNU_PROPERTY .pushsection ".note.gnu.property", "a" SEPARATOR \ .balign 8 SEPARATOR \ .long 4 SEPARATOR \ @@ -91,12 +106,12 @@ .asciz "GNU" SEPARATOR \ .long 0xc0000000 SEPARATOR /* GNU_PROPERTY_AARCH64_FEATURE_1_AND */ \ .long 4 SEPARATOR \ - .long 3 SEPARATOR /* GNU_PROPERTY_AARCH64_FEATURE_1_BTI AND */ \ - /* GNU_PROPERTY_AARCH64_FEATURE_1_PAC */ \ + .long GNU_PROPERTY SEPARATOR \ .long 0 SEPARATOR \ .popsection SEPARATOR -#define AARCH64_BTI bti c -#else +#endif +#endif +#if !defined(AARCH64_BTI) #define AARCH64_BTI #endif `````````` </details> https://github.com/llvm/llvm-project/pull/102322 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
