Formerly GDB tried to show what it can. Nowadays with GCC VTA it should hide values which may be / are corrupted as it may be misleading. DWARF2_FRAME_REG_UNSPECIFIED is currently equal to DWARF2_FRAME_REG_SAME_VALUE. DWARF2_FRAME_REG_UNSPECIFIED should respect target arch caller-saved vs. callee-saved registers map and mark caller-saved registers as unknown (which is currently only possible by DWARF2_FRAME_REG_UNDEFINED and thus frame_unwind_got_optimized which is not completely right but it would work). FAIL all these: gcc (GCC) 4.6.0 20100724 (experimental) gcc (GCC) 4.4.5 20100724 (prerelease) gcc-4.4.4-10.fc13.x86_64 GNU gdb (GDB) 7.2.50.20100724-cvs #0 breakat (q=0) at 1.c:7 #1 0x000000000040053b in f (a1=<value optimized out>, a2=2, a3=3, a4=4, a5=5, a6=6, a7=7) at 2.c:6 #2 0x00000000004004fc in g (x=0) at 1.c:14 ^^^ x=10 here, it should be <value optimized out> #3 0x000000000040051e in main () at 2.c:14 ==> 1.c <== #include <stdlib.h> extern __attribute__((noreturn)) void f (long a1, long a2, long a3, long a4, long a5, long a6, long a7); __attribute__((noreturn)) void breakat (long q) { exit (0); } __attribute__((noinline)) void g (long x) { f (x, 2, 3, 4, 5, 6, 7); } ==> 2.c <== extern __attribute__((noreturn)) void breakat (long q); __attribute__((noreturn)) void f (long a1, long a2, long a3, long a4, long a5, long a6, long a7) { breakat (0); } extern __attribute__((noinline)) void g (long x); int main (void) { g (10); return 0; }
Created attachment 4883 [details] .s files for x86_64-unknown-linux-gnu.
Filed as GCC PR: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45103 According to Jakub Jelinek there are GCC options -ffixed-X, -fcall-used-X which may change the ABI-specified caller/callee-saved register set. Jakub has a GCC patch for this Bug.