+2000-03-04 Mark Kettenis <kettenis@gnu.org>
+
+ Fix support for Linux/i386 signal trampolines. The old approach
+ didn't work for Linux 2.2 and beyond, and didn't work with recent
+ versions of the GNU C library.
+ * i386-tdep.c (LINUX_RT_SIGTRAMP_INSN0, LINUX_RT_SIGTRAMP_OFFSET0,
+ LINUX_RT_SIGTRAMP_INSN1, LINUX_RT_SIGTRAMP_OFFSET1): New defines.
+ (linux_rt_sigtramp_code): New variable.
+ (LINUX_RT_SIGTRAMP_LEN): New define.
+ (i386_linux_rt_sigtramp_start): New function. Detect start of
+ signal trampolines for RT signals.
+ (i386_linux_sigtramp): Removed.
+ (i386_linux_in_sigtramp): New function.
+ (i386_linux_sigcontext_addr): New function. Recognize the names
+ of the signal tranmpolines used by recent versions of the GNU C
+ library, and add support for RT signals.
+ (LINUX_SIGCONTEXT_PC_OFFSET, LINUX_SIGCONTEXT_SP_OFFSET): New
+ defines. Moved here from config/i386/tm-linux.h.
+ (i386_linux_sigtramp_saved_pc, i386_linux_sigtramp_saved_sp):
+ Reimplement in terms of i386_linux_sigcontext_addr.
+ * config/i386/tm-linux.h (LINUX_SIGCONTEXT_SIZE): Removed.
+ (LINUX_SIGCONTEXT_PC_OFFSET, LINUX_SIGCONTEXT_SP_OFFSET):
+ Moved to i386-tdep.c.
+ (IN_SIGTRAMP): Redefine to call i386_linux_in_sigtramp.
+
Sat Mar 4 19:38:11 2000 Andrew Cagney <cagney@b1.cygnus.com>
By: Sat Mar 4 04:08:58 2000 Alexandre Oliva <oliva@lsd.ic.unicamp.br>
#include "i386/tm-i386.h"
#include "tm-linux.h"
-/* Size of sigcontext, from <asm/sigcontext.h>. */
-#define LINUX_SIGCONTEXT_SIZE (88)
-
-/* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */
-#define LINUX_SIGCONTEXT_PC_OFFSET (56)
-
-/* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */
-#define LINUX_SIGCONTEXT_SP_OFFSET (28)
-
#define LOW_RETURN_REGNUM 0 /* holds low four bytes of result */
#define HIGH_RETURN_REGNUM 2 /* holds high four bytes of result */
order to support backtracing through calls to signal handlers. */
#define I386_LINUX_SIGTRAMP
-#define IN_SIGTRAMP(pc, name) ((name) == NULL && i386_linux_sigtramp (pc))
-
-extern int i386_linux_sigtramp PARAMS ((CORE_ADDR));
+#define IN_SIGTRAMP(pc, name) i386_linux_in_sigtramp (pc, name)
+extern int i386_linux_in_sigtramp (CORE_ADDR, char *);
/* We need our own version of sigtramp_saved_pc to get the saved PC in
a sigtramp routine. */
#define sigtramp_saved_pc i386_linux_sigtramp_saved_pc
-extern CORE_ADDR i386_linux_sigtramp_saved_pc PARAMS ((struct frame_info *));
+extern CORE_ADDR i386_linux_sigtramp_saved_pc (struct frame_info *);
/* Signal trampolines don't have a meaningful frame. As in tm-i386.h,
the frame pointer value we use is actually the frame pointer of the
? read_memory_integer (i386_linux_sigtramp_saved_sp ((FRAME)->next), 4) \
: read_memory_integer ((FRAME)->frame + 4, 4)))
-extern CORE_ADDR i386_linux_sigtramp_saved_sp PARAMS ((struct frame_info *));
+extern CORE_ADDR i386_linux_sigtramp_saved_sp (struct frame_info *);
/* When we call a function in a shared library, and the PLT sends us
into the dynamic linker to find the function's real address, we
#ifdef I386_LINUX_SIGTRAMP
-/* When the i386 Linux kernel calls a signal handler, the return
- address points to a bit of code on the stack. This function
- returns whether the PC appears to be within this bit of code.
-
- The instruction sequence is
+/* Linux has two flavors of signals. Normal signal handlers, and
+ "realtime" (RT) signals. The RT signals can provide additional
+ information to the signal handler if the SA_SIGINFO flag is set
+ when establishing a signal handler using `sigaction'. It is not
+ unlikely that future versions of Linux will support SA_SIGINFO for
+ normal signals too. */
+
+/* When the i386 Linux kernel calls a signal handler and the
+ SA_RESTORER flag isn't set, the return address points to a bit of
+ code on the stack. This function returns whether the PC appears to
+ be within this bit of code.
+
+ The instruction sequence for normal signals is
pop %eax
mov $0x77,%eax
int $0x80
order to identify a signal trampoline, but there doesn't seem to be
any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to
only call us if no function name could be identified, which should
- be the case since the code is on the stack. */
+ be the case since the code is on the stack.
+
+ Detection of signal trampolines for handlers that set the
+ SA_RESTORER flag is in general not possible. Unfortunately this is
+ what the GNU C Library has been doing for quite some time now.
+ However, as of version 2.1.2, the GNU C Library uses signal
+ trampolines (named __restore and __restore_rt) that are identical
+ to the ones used by the kernel. Therefore, these trampolines are
+ supported too. */
#define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */
#define LINUX_SIGTRAMP_OFFSET0 (0)
the routine. Otherwise, return 0. */
static CORE_ADDR
-i386_linux_sigtramp_start (pc)
- CORE_ADDR pc;
+i386_linux_sigtramp_start (CORE_ADDR pc)
{
unsigned char buf[LINUX_SIGTRAMP_LEN];
return pc;
}
+/* This function does the same for RT signals. Here the instruction
+ sequence is
+ mov $0xad,%eax
+ int $0x80
+ or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80.
+
+ The effect is to call the system call rt_sigreturn. */
+
+#define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */
+#define LINUX_RT_SIGTRAMP_OFFSET0 (0)
+#define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */
+#define LINUX_RT_SIGTRAMP_OFFSET1 (5)
+
+static const unsigned char linux_rt_sigtramp_code[] =
+{
+ LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */
+ LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */
+};
+
+#define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code)
+
+/* If PC is in a RT sigtramp routine, return the address of the start
+ of the routine. Otherwise, return 0. */
+
+static CORE_ADDR
+i386_linux_rt_sigtramp_start (CORE_ADDR pc)
+{
+ unsigned char buf[LINUX_RT_SIGTRAMP_LEN];
+
+ /* We only recognize a signal trampoline if PC is at the start of
+ one of the two instructions. We optimize for finding the PC at
+ the start, as will be the case when the trampoline is not the
+ first frame on the stack. We assume that in the case where the
+ PC is not at the start of the instruction sequence, there will be
+ a few trailing readable bytes on the stack. */
+
+ if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0)
+ return 0;
+
+ if (buf[0] != LINUX_RT_SIGTRAMP_INSN0)
+ {
+ if (buf[0] != LINUX_RT_SIGTRAMP_INSN1)
+ return 0;
+
+ pc -= LINUX_RT_SIGTRAMP_OFFSET1;
+
+ if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0)
+ return 0;
+ }
+
+ if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0)
+ return 0;
+
+ return pc;
+}
+
/* Return whether PC is in a Linux sigtramp routine. */
int
-i386_linux_sigtramp (pc)
- CORE_ADDR pc;
+i386_linux_in_sigtramp (CORE_ADDR pc, char *name)
{
- return i386_linux_sigtramp_start (pc) != 0;
+ if (name)
+ return STREQ ("__restore", name) || STREQ ("__restore_rt", name);
+
+ return (i386_linux_sigtramp_start (pc) != 0
+ || i386_linux_rt_sigtramp_start (pc) != 0);
}
-/* Assuming FRAME is for a Linux sigtramp routine, return the saved
- program counter. The Linux kernel will set up a sigcontext
- structure immediately before the sigtramp routine on the stack. */
+/* Assuming FRAME is for a Linux sigtramp routine, return the address
+ of the associated sigcontext structure. */
CORE_ADDR
-i386_linux_sigtramp_saved_pc (frame)
- struct frame_info *frame;
+i386_linux_sigcontext_addr (struct frame_info *frame)
{
CORE_ADDR pc;
pc = i386_linux_sigtramp_start (frame->pc);
- if (pc == 0)
- error ("i386_linux_sigtramp_saved_pc called when no sigtramp");
- return read_memory_integer ((pc
- - LINUX_SIGCONTEXT_SIZE
- + LINUX_SIGCONTEXT_PC_OFFSET),
- 4);
+ if (pc)
+ {
+ CORE_ADDR sp;
+
+ if (frame->next)
+ /* If this isn't the top frame, the next frame must be for the
+ signal handler itself. The sigcontext structure lives on
+ the stack, right after the signum argument. */
+ return frame->next->frame + 12;
+
+ /* This is the top frame. We'll have to find the address of the
+ sigcontext structure by looking at the stack pointer. Keep
+ in mind that the first instruction of the sigtramp code is
+ "pop %eax". If the PC is at this instruction, adjust the
+ returned value accordingly. */
+ sp = read_register (SP_REGNUM);
+ if (pc == frame->pc)
+ return sp + 4;
+ return sp;
+ }
+
+ pc = i386_linux_rt_sigtramp_start (frame->pc);
+ if (pc)
+ {
+ if (frame->next)
+ /* If this isn't the top frame, the next frame must be for the
+ signal handler itself. The sigcontext structure is part of
+ the user context. A pointer to the user context is passed
+ as the third argument to the signal handler. */
+ return read_memory_integer (frame->next->frame + 16, 4) + 20;
+
+ /* This is the top frame. Again, use the stack pointer to find
+ the address of the sigcontext structure. */
+ return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20;
+ }
+
+ error ("Couldn't recognize signal trampoline.");
+ return 0;
}
+/* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */
+#define LINUX_SIGCONTEXT_PC_OFFSET (56)
+
/* Assuming FRAME is for a Linux sigtramp routine, return the saved
- stack pointer. The Linux kernel will set up a sigcontext structure
- immediately before the sigtramp routine on the stack. */
+ program counter. */
CORE_ADDR
-i386_linux_sigtramp_saved_sp (frame)
- struct frame_info *frame;
+i386_linux_sigtramp_saved_pc (struct frame_info *frame)
{
- CORE_ADDR pc;
+ CORE_ADDR addr;
+ addr = i386_linux_sigcontext_addr (frame);
+ return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4);
+}
- pc = i386_linux_sigtramp_start (frame->pc);
- if (pc == 0)
- error ("i386_linux_sigtramp_saved_sp called when no sigtramp");
- return read_memory_integer ((pc
- - LINUX_SIGCONTEXT_SIZE
- + LINUX_SIGCONTEXT_SP_OFFSET),
- 4);
+/* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */
+#define LINUX_SIGCONTEXT_SP_OFFSET (28)
+
+/* Assuming FRAME is for a Linux sigtramp routine, return the saved
+ stack pointer. */
+
+CORE_ADDR
+i386_linux_sigtramp_saved_sp (struct frame_info *frame)
+{
+ CORE_ADDR addr;
+ addr = i386_linux_sigcontext_addr (frame);
+ return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4);
}
#endif /* I386_LINUX_SIGTRAMP */
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