Do not read syscall no in get_scno_on_sysexit

* syscall.c (get_scno_on_sysexit): Remove scno retrieval code, since
we don't save it anyway. This is the first real logic change
which should make strace faster: for example, on x64 ORIG_EAX
is no longer read in each syscall exit.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

diff --git a/syscall.c b/syscall.c
index a3b6080901f87b13d64ba16b72243522bef53e75..a6f47af42d6fff881e4ac56a64258d165403d945 100644 (file)
--- a/syscall.c
+++ b/syscall.c
@@ -1296,124 +1296,18 @@ get_scno_on_sysenter(struct tcb *tcp)
 static int
 get_scno_on_sysexit(struct tcb *tcp)
 {
-       long scno = 0;
-
 #ifdef LINUX
 # if defined(S390) || defined(S390X)
-       if (tcp->flags & TCB_WAITEXECVE) {
-               /*
-                * When the execve system call completes successfully, the
-                * new process still has -ENOSYS (old style) or __NR_execve
-                * (new style) in gpr2.  We cannot recover the scno again
-                * by disassembly, because the image that executed the
-                * syscall is gone now.  Fortunately, we don't want it.  We
-                * leave the flag set so that syscall_fixup can fake the
-                * result.
-                */
-               return 1;
-       }
-
-       if (upeek(tcp, PT_GPR2, &syscall_mode) < 0)
-               return -1;
-
-       if (syscall_mode != -ENOSYS) {
-               /*
-                * Since kernel version 2.5.44 the scno gets passed in gpr2.
-                */
-               scno = syscall_mode;
-       } else {
-               /*
-                * Old style of "passing" the scno via the SVC instruction.
-                */
-
-               long opcode, offset_reg, tmp;
-               void * svc_addr;
-               static const int gpr_offset[16] = {
-                               PT_GPR0,  PT_GPR1,  PT_ORIGGPR2, PT_GPR3,
-                               PT_GPR4,  PT_GPR5,  PT_GPR6,     PT_GPR7,
-                               PT_GPR8,  PT_GPR9,  PT_GPR10,    PT_GPR11,
-                               PT_GPR12, PT_GPR13, PT_GPR14,    PT_GPR15
-               };
-
-               if (upeek(tcp, PT_PSWADDR, &pc) < 0)
-                       return -1;
-               errno = 0;
-               opcode = ptrace(PTRACE_PEEKTEXT, tcp->pid, (char *)(pc-sizeof(long)), 0);
-               if (errno) {
-                       perror("peektext(pc-oneword)");
-                       return -1;
-               }
-
-               /*
-                *  We have to check if the SVC got executed directly or via an
-                *  EXECUTE instruction. In case of EXECUTE it is necessary to do
-                *  instruction decoding to derive the system call number.
-                *  Unfortunately the opcode sizes of EXECUTE and SVC are differently,
-                *  so that this doesn't work if a SVC opcode is part of an EXECUTE
-                *  opcode. Since there is no way to find out the opcode size this
-                *  is the best we can do...
-                */
-
-               if ((opcode & 0xff00) == 0x0a00) {
-                       /* SVC opcode */
-                       scno = opcode & 0xff;
-               }
-               else {
-                       /* SVC got executed by EXECUTE instruction */
-
-                       /*
-                        *  Do instruction decoding of EXECUTE. If you really want to
-                        *  understand this, read the Principles of Operations.
-                        */
-                       svc_addr = (void *) (opcode & 0xfff);
-
-                       tmp = 0;
-                       offset_reg = (opcode & 0x000f0000) >> 16;
-                       if (offset_reg && (upeek(tcp, gpr_offset[offset_reg], &tmp) < 0))
-                               return -1;
-                       svc_addr += tmp;
-
-                       tmp = 0;
-                       offset_reg = (opcode & 0x0000f000) >> 12;
-                       if (offset_reg && (upeek(tcp, gpr_offset[offset_reg], &tmp) < 0))
-                               return -1;
-                       svc_addr += tmp;
-
-                       scno = ptrace(PTRACE_PEEKTEXT, tcp->pid, svc_addr, 0);
-                       if (errno)
-                               return -1;
-#  if defined(S390X)
-                       scno >>= 48;
-#  else
-                       scno >>= 16;
-#  endif
-                       tmp = 0;
-                       offset_reg = (opcode & 0x00f00000) >> 20;
-                       if (offset_reg && (upeek(tcp, gpr_offset[offset_reg], &tmp) < 0))
-                               return -1;
-
-                       scno = (scno | tmp) & 0xff;
-               }
-       }
 # elif defined (POWERPC)
-       if (upeek(tcp, sizeof(unsigned long)*PT_R0, &scno) < 0)
-               return -1;
 # elif defined(AVR32)
        /*
         * Read complete register set in one go.
         */
        if (ptrace(PTRACE_GETREGS, tcp->pid, NULL, &regs) < 0)
                return -1;
-
 # elif defined(BFIN)
-       if (upeek(tcp, PT_ORIG_P0, &scno))
-               return -1;
 # elif defined (I386)
-       if (upeek(tcp, 4*ORIG_EAX, &scno) < 0)
-               return -1;
 # elif defined (X86_64)
-       if (upeek(tcp, 8*ORIG_RAX, &scno) < 0)
-               return -1;
 # elif defined(IA64)
 #      define IA64_PSR_IS      ((long)1 << 34)
        if (upeek(tcp, PT_CR_IPSR, &psr) >= 0)
@@ -1428,71 +1322,7 @@ get_scno_on_sysexit(struct tcb *tcp)
         */
        if (ptrace(PTRACE_GETREGS, tcp->pid, NULL, (void *)&regs) == -1)
                return -1;
-
-       /*
-        * We only need to grab the syscall number on syscall entry.
-        */
-       if (regs.ARM_ip == 0) {
-               /*
-                * Note: we only deal with only 32-bit CPUs here.
-                */
-               if (regs.ARM_cpsr & 0x20) {
-                       /*
-                        * Get the Thumb-mode system call number
-                        */
-                       scno = regs.ARM_r7;
-               } else {
-                       /*
-                        * Get the ARM-mode system call number
-                        */
-                       errno = 0;
-                       scno = ptrace(PTRACE_PEEKTEXT, tcp->pid, (void *)(regs.ARM_pc - 4), NULL);
-                       if (errno)
-                               return -1;
-
-               /* FIXME: bogus check? it is already done on entering before,
-                * so we never can see it here?
-                */
-                       if (scno == 0 && (tcp->flags & TCB_WAITEXECVE)) {
-                               tcp->flags &= ~TCB_WAITEXECVE;
-                               return 0;
-                       }
-
-                       /* Handle the EABI syscall convention.  We do not
-                          bother converting structures between the two
-                          ABIs, but basic functionality should work even
-                          if strace and the traced program have different
-                          ABIs.  */
-                       if (scno == 0xef000000) {
-                               scno = regs.ARM_r7;
-                       } else {
-                               if ((scno & 0x0ff00000) != 0x0f900000) {
-                                       fprintf(stderr, "syscall: unknown syscall trap 0x%08lx\n",
-                                               scno);
-                                       return -1;
-                               }
-
-                               /*
-                                * Fixup the syscall number
-                                */
-                               scno &= 0x000fffff;
-                       }
-               }
-               if (scno & 0x0f0000) {
-                       /*
-                        * Handle ARM specific syscall
-                        */
-                       set_personality(1);
-                       scno &= 0x0000ffff;
-               } else
-                       set_personality(0);
-
-               fprintf(stderr, "pid %d stray syscall exit\n", tcp->pid);
-               tcp->flags &= ~TCB_INSYSCALL;
-       }
 # elif defined (M68K)
-       if (upeek(tcp, 4*PT_ORIG_D0, &scno) < 0)
-               return -1;
 # elif defined (LINUX_MIPSN32)
        unsigned long long regs[38];
 
@@ -1515,47 +1345,15 @@ get_scno_on_sysexit(struct tcb *tcp)
        if (ptrace(PTRACE_GETREGS, tcp->pid, (char *)&regs, 0) < 0)
                return -1;
 # elif defined(HPPA)
-       if (upeek(tcp, PT_GR20, &scno) < 0)
-               return -1;
 # elif defined(SH)
-       /*
-        * In the new syscall ABI, the system call number is in R3.
-        */
-       if (upeek(tcp, 4*(REG_REG0+3), &scno) < 0)
-               return -1;
-
-       if (scno < 0) {
-               /* Odd as it may seem, a glibc bug has been known to cause
-                  glibc to issue bogus negative syscall numbers.  So for
-                  our purposes, make strace print what it *should* have been */
-               long correct_scno = (scno & 0xff);
-               if (debug)
-                       fprintf(stderr,
-                               "Detected glibc bug: bogus system call"
-                               " number = %ld, correcting to %ld\n",
-                               scno,
-                               correct_scno);
-               scno = correct_scno;
-       }
 # elif defined(SH64)
-       if (upeek(tcp, REG_SYSCALL, &scno) < 0)
-               return -1;
-       scno &= 0xFFFF;
 # elif defined(CRISV10) || defined(CRISV32)
-       if (upeek(tcp, 4*PT_R9, &scno) < 0)
-               return -1;
 # elif defined(TILE)
-       if (upeek(tcp, PTREGS_OFFSET_REG(10), &scno) < 0)
-               return -1;
 # elif defined(MICROBLAZE)
-       if (upeek(tcp, 0, &scno) < 0)
-               return -1;
 # endif
 #endif /* LINUX */
 
 #ifdef SUNOS4
-       if (upeek(tcp, uoff(u_arg[7]), &scno) < 0)
-               return -1;
 #elif defined(SH)
        /* new syscall ABI returns result in R0 */
        if (upeek(tcp, 4*REG_REG0, (long *)&r0) < 0)
@@ -1567,25 +1365,12 @@ get_scno_on_sysexit(struct tcb *tcp)
 #endif
 
 #ifdef USE_PROCFS
-# ifdef HAVE_PR_SYSCALL
-       scno = tcp->status.PR_SYSCALL;
-# else
-#  ifndef FREEBSD
-       scno = tcp->status.PR_WHAT;
-#  else
+# ifndef HAVE_PR_SYSCALL
+#  ifdef FREEBSD
        if (pread(tcp->pfd_reg, &regs, sizeof(regs), 0) < 0) {
                perror("pread");
                return -1;
        }
-       switch (regs.r_eax) {
-       case SYS_syscall:
-       case SYS___syscall:
-               pread(tcp->pfd, &scno, sizeof(scno), regs.r_esp + sizeof(int));
-               break;
-       default:
-               scno = regs.r_eax;
-               break;
-       }
 #  endif /* FREEBSD */
 # endif /* !HAVE_PR_SYSCALL */
 #endif /* USE_PROCFS */