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Well it's ages since I sent anything to gdb-patches I hope that someone's still listening! GDB (971126 snapshot, presumably earlier versions) doesn't unwind the stack correctly through signal handler invocations - the following patch corrects things diff -r -u orig/gdb-971126/gdb/ChangeLog gdb-971126/gdb/ChangeLog --- orig/gdb-971126/gdb/ChangeLog Wed Nov 26 16:48:11 1997 +++ gdb-971126/gdb/ChangeLog Sun Jan 18 16:21:34 1998 @@ -1,3 +1,8 @@ +1998-01-18 Paul Flinders <paul@dawa.demon.co.uk> + + * config/i386/tm-linux.h(IN_SIGTRAMP, FRAME_SAVED_PC) Add support + for correctly unwinding through Linux signal handlers + Wed Nov 26 09:59:47 1997 Andrew Cagney <cagney@b1.cygnus.com> * dwarf2read.c (struct comp_unit_head): Change length and diff -r -u orig/gdb-971126/gdb/config/i386/tm-linux.h gdb-971126/gdb/config/i386/tm-linux.h --- orig/gdb-971126/gdb/config/i386/tm-linux.h Wed Nov 26 16:28:29 1997 +++ gdb-971126/gdb/config/i386/tm-linux.h Sun Jan 18 16:18:14 1998 @@ -25,15 +25,39 @@ #include "i386/tm-i386.h" -/* Offset to saved PC in sigcontext, from <linux/signal.h>. */ -#define SIGCONTEXT_PC_OFFSET 38 - /* We need this file for the SOLIB_TRAMPOLINE stuff. */ #include "tm-sysv4.h" /* The following works around a problem with /usr/include/sys/procfs.h */ #define sys_quotactl + +/* Linux calls signal handlers as handler(int signo, struct sigcontext sc) + rather than the bsd style of (int signo, int code, struct sigcontext *sc) so + the default sigtramp_saved_pc in blockframe.c doesn't work. Also there's no + sigtramp function - a return trampoline is placed in the stack by the kernel. + + So we detect the trampoline by disassembling the code and replace the + version of FRAME_SAVED_PC from i386/tm-i386.h with the one below. We use the + fact that the return trampoline immediately follows the sigcontext structure + in memory to get the location of the saved PC */ + +#define IN_SIGTRAMP(pc, name) \ + (read_memory_unsigned_integer (pc, 1) == 0x58 /* popl %eax */ \ + && read_memory_unsigned_integer (pc+1, 1) == 0xb8 /* movl $,eax */ \ + && read_memory_unsigned_integer (pc+2, 4) == 0x77 /* $= 0x77 (sigret) */ \ + && read_memory_unsigned_integer (pc+6, 2) == 0x80cd) /* int 80 */ + +#undef FRAME_SAVED_PC + +/* Saved Pc. Get it from sigcontext if within sigtramp. */ +#define FRAME_SAVED_PC(FRAME) \ + (((FRAME)->signal_handler_caller \ + ? read_memory_integer ((FRAME)->pc - 32, 4) \ + : read_memory_integer ((FRAME)->frame + 4, 4)) \ + ) + + #endif /* #ifndef TM_LINUX_H */