From 0c75ebaad09d6d3f2395dfe6160904af883dd0d9 Mon Sep 17 00:00:00 2001 From: Andre McCurdy Date: Tue, 15 May 2018 15:34:39 -0700 Subject: [PATCH] linux/arm/raw_syscall.h: avoid r7 specified register variables with Thumb If Thumb code is being generated and frame pointers are enabled, the Thumb frame pointer in r7 clashes with any local variable which may need to be assigned to r7 (e.g. the syscall NR when making a raw syscall). With gcc, the double use of r7 results in a build error, e.g. strace-4.22/tests/inject-nf.c:86:1: error: r7 cannot be used in asm here With clang, the double use of r7 can result in the compiler silently generating broken code which crashes at run time due to frame pointer corruption: https://bugs.llvm.org/show_bug.cgi?id=34165 In most cases the problem isn't visible as frame pointers will be disabled automatically due to optimisation level. However to handle cases where frame pointers are enabled (e.g. when CFLAGS etc are set to support a debug build, etc) provide a version of raw_syscall_0 which manually saves and restores the frame pointer value in r7 to a temporary register before setting up the syscall NR in r7 and invoking the syscall. * linux/arm/raw_syscall.h (raw_syscall_0) [__thumb__]: Provide an alternative version. Upstream-Status: Backport Signed-off-by: Andre McCurdy --- linux/arm/raw_syscall.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/linux/arm/raw_syscall.h b/linux/arm/raw_syscall.h index 69c7e23..ec534ec 100644 --- a/linux/arm/raw_syscall.h +++ b/linux/arm/raw_syscall.h @@ -36,12 +36,27 @@ static inline kernel_ulong_t raw_syscall_0(const kernel_ulong_t nr, kernel_ulong_t *err) { *err = 0; + +#ifdef __thumb__ /* && FRAME_POINTERS_ENABLED */ + + register kernel_ulong_t rt; + register kernel_ulong_t r0 __asm__("r0"); + __asm__ __volatile__("mov %1,r7; mov r7,%2; swi 0x0; mov r7,%1" + : "=r"(r0), "=&r"(rt) + : "r"(nr) + : "memory"); + +#else + register kernel_ulong_t r7 __asm__("r7") = nr; register kernel_ulong_t r0 __asm__("r0"); __asm__ __volatile__("swi 0x0" : "=r"(r0) : "r"(r7) : "memory"); + +#endif + return r0; } # define raw_syscall_0 raw_syscall_0 -- 1.9.1