[Valgrind-developers] [PATCH for valgrind] coregrind: implement GS override for arch_prctl on linux

[Maarten L. <m.b...@gm...>]

Allows wine64 to start in valgrind! Apply with -Np0. :D

Yes I know that %gs is still zero on linux amd64. Details details..

Signed-off-by: Maarten Lankhorst <maa...@ub...>

---

FWIW, wine64 is still failing, it's unable to decode some instructions in the save_context (and presumable set_cpu_context) functions.

Specifically some calls from RtlCaptureContext:

    7bc869c0:   8c 49 38                mov    %cs,0x38(%rcx)
    7bc869c3:   8c 59 3a                mov    %ds,0x3a(%rcx)
    7bc869c6:   8c 41 3c                mov    %es,0x3c(%rcx)
    7bc869c9:   8c 61 3e                mov    %fs,0x3e(%rcx)
    7bc869cc:   8c 69 40                mov    %gs,0x40(%rcx)
    7bc869cf:   8c 51 42                mov    %ss,0x42(%rcx)

afaict, it should be fair to assume that fs and gs will always be 0 here. It looks like ds, es and ss will not be restored directly,
instead the set_cpu_context wine call uses iretq to restore the cpu context. valgrind's instruction decoder probably will not work with that either.
Would someone be willing to look at this?

Index: coregrind/m_translate.c
===================================================================
--- coregrind/m_translate.c	(revision 13279)
+++ coregrind/m_translate.c	(working copy)
@@ -1486,7 +1486,7 @@
 #  if defined(VGP_amd64_linux)
    vex_abiinfo.guest_amd64_assume_fs_is_zero  = True;
 #  endif
-#  if defined(VGP_amd64_darwin)
+#  if defined(VGP_amd64_darwin) || defined(VGP_amd64_linux)
    vex_abiinfo.guest_amd64_assume_gs_is_0x60  = True;
 #  endif
 #  if defined(VGP_ppc32_linux)
Index: coregrind/m_syswrap/syswrap-amd64-linux.c
===================================================================
--- coregrind/m_syswrap/syswrap-amd64-linux.c	(revision 13279)
+++ coregrind/m_syswrap/syswrap-amd64-linux.c	(working copy)
@@ -564,6 +564,16 @@
       *(unsigned long *)ARG2 = tst->arch.vex.guest_FS_ZERO;
       POST_MEM_WRITE(ARG2, sizeof(unsigned long));
    }
+   else if (ARG1 == VKI_ARCH_SET_GS) {
+      tst = VG_(get_ThreadState)(tid);
+      tst->arch.vex.guest_GS_0x60 = ARG2;
+   }
+   else if (ARG1 == VKI_ARCH_GET_GS) {
+      PRE_MEM_WRITE("arch_prctl(addr)", ARG2, sizeof(unsigned long));
+      tst = VG_(get_ThreadState)(tid);
+      *(unsigned long *)ARG2 = tst->arch.vex.guest_GS_0x60;
+      POST_MEM_WRITE(ARG2, sizeof(unsigned long));
+   }
    else {
       VG_(core_panic)("Unsupported arch_prtctl option");
    }