[valgrind] [Bug 506910] openat2 with RESOLVE_NO_MAGICLINKS succeeds on /proc/self/exe

[Mark Wielaard]

https://bugs.kde.org/show_bug.cgi?id=506910

--- Comment #2 from Mark Wielaard <m...@klomp.org> ---
The issue seems to be that at the end of sys_openat2 if we detected it was
called on proc_self_exe then we want to force the syscall with
VG_(resolved_exename) as ARG2 and SET_STATUS_from_SysRes. But then fall through
to where we set flags to contain SfMayBlock. 

We could do an immediate return after:
      // do the syscall with VG_(resolved_exename)                              
      SET_STATUS_from_SysRes(VG_(do_syscall4)(SYSNO, ARG1,
(Word)VG_(resolved_exename), ARG3, ARG4));
      return;

But since it is the same syscall it seems simpler to just modify ARG2 and fall
through.

Testing the following patch:

diff --git a/coregrind/m_syswrap/syswrap-linux.c
b/coregrind/m_syswrap/syswrap-linux.c
index e16d293cd08f..1499e75bccf0 100644
--- a/coregrind/m_syswrap/syswrap-linux.c
+++ b/coregrind/m_syswrap/syswrap-linux.c
@@ -6094,7 +6094,7 @@ no_client_write:
    if (proc_self_exe) {

       // do the syscall with VG_(resolved_exename)
-      SET_STATUS_from_SysRes(VG_(do_syscall4)(SYSNO, ARG1,
(Word)VG_(resolved_exename), ARG3, ARG4));
+      ARG2 = (Word)VG_(resolved_exename);
    }

    /* Otherwise handle normally */
@@ -14095,7 +14095,8 @@ PRE(sys_openat2)
    if (proc_self_exe) {

       // do the syscall with VG_(resolved_exename)
-      SET_STATUS_from_SysRes(VG_(do_syscall4)(SYSNO, ARG1,
(Word)VG_(resolved_exename), ARG3, ARG4));
+      ARG2 = (Word)VG_(resolved_exename);
+
    }

    /* Otherwise handle normally */

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