diff options
Diffstat (limited to 'gdb/i386-linux-nat.c')
| -rw-r--r-- | gdb/i386-linux-nat.c | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/gdb/i386-linux-nat.c b/gdb/i386-linux-nat.c index 93ea241..2bfac29 100644 --- a/gdb/i386-linux-nat.c +++ b/gdb/i386-linux-nat.c @@ -951,6 +951,91 @@ fetch_core_registers (char *core_reg_sect, unsigned core_reg_size, } +/* The instruction for a Linux system call is: + int $0x80 + or 0xcd 0x80. */ + +static const unsigned char linux_syscall[] = { 0xcd, 0x80 }; + +#define LINUX_SYSCALL_LEN (sizeof linux_syscall) + +/* The system call number is stored in the %eax register. */ +#define LINUX_SYSCALL_REGNUM 0 /* %eax */ + +/* We are specifically interested in the sigreturn and rt_sigreturn + system calls. */ + +#ifndef SYS_sigreturn +#define SYS_sigreturn 0x77 +#endif +#ifndef SYS_rt_sigreturn +#define SYS_rt_sigreturn 0xad +#endif + +/* Offset to saved processor flags, from <asm/sigcontext.h>. */ +#define LINUX_SIGCONTEXT_EFLAGS_OFFSET (64) + +/* Resume execution of the inferior process. + If STEP is nonzero, single-step it. + If SIGNAL is nonzero, give it that signal. */ + +void +child_resume (int pid, int step, enum target_signal signal) +{ + int request = PTRACE_CONT; + + if (pid == -1) + /* Resume all threads. */ + /* I think this only gets used in the non-threaded case, where "resume + all threads" and "resume inferior_pid" are the same. */ + pid = inferior_pid; + + if (step) + { + CORE_ADDR pc = read_pc_pid (pid); + unsigned char buf[LINUX_SYSCALL_LEN]; + + request = PTRACE_SINGLESTEP; + + /* Returning from a signal trampoline is done by calling a + special system call (sigreturn or rt_sigreturn, see + i386-linux-tdep.c for more information). This system call + restores the registers that were saved when the signal was + raised, including %eflags. That means that single-stepping + won't work. Instead, we'll have to modify the signal context + that's about to be restored, and set the trace flag there. */ + + /* First check if PC is at a system call. */ + if (read_memory_nobpt (pc, (char *) buf, LINUX_SYSCALL_LEN) == 0 + && memcmp (buf, linux_syscall, LINUX_SYSCALL_LEN) == 0) + { + int syscall = read_register_pid (LINUX_SYSCALL_REGNUM, pid); + + /* Then check the system call number. */ + if (syscall == SYS_sigreturn || syscall == SYS_rt_sigreturn) + { + CORE_ADDR sp = read_register (SP_REGNUM); + CORE_ADDR addr = sp; + unsigned long int eflags; + + if (syscall == SYS_rt_sigreturn) + addr = read_memory_integer (sp + 8, 4) + 20; + + /* Set the trace flag in the context that's about to be + restored. */ + addr += LINUX_SIGCONTEXT_EFLAGS_OFFSET; + read_memory (addr, (char *) &eflags, 4); + eflags |= 0x0100; + write_memory (addr, (char *) &eflags, 4); + } + } + } + + if (ptrace (request, pid, 0, target_signal_to_host (signal)) == -1) + perror_with_name ("ptrace"); +} + + /* Calling functions in shared libraries. */ /* FIXME: kettenis/2000-03-05: Doesn't this belong in a target-dependent file? The function |