[Bug ld/29226] gcc -fcf-protection option causes GCC 12 gccgo build to fail : "failed to match split-stack sequence"

[jason.vas.dias at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29226

Jason Vas Dias <jason.vas.dias at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P2                          |P1
                 CC|                            |jason.vas.dias at gmail dot com

--- Comment #13 from Jason Vas Dias <jason.vas.dias at gmail dot com> ---
OK, I discovered the SAME test fails completely without either of my
patches, but BOTH allow the particular GCC build I was trying to succeed -
I'm going with the last one :

---BEGIN PATCH
diff -up gold/i386.cc~ gold/i386.cc
--- gold/i386.cc~       2022-06-05 02:23:38.826984954 +0100
+++ gold/i386.cc        2022-06-05 18:16:55.215927752 +0100
@@ -4190,12 +4190,34 @@ Target_i386::do_calls_non_split(Relobj*
       elfcpp::Swap_unaligned<32, false>::writeval(pval, val);
     }
   else
-    {
-      if (!object->has_no_split_stack())
+    { bool is_rdssp = this->match_view(view, view_size, fnoffset,
"\xf3\x0f\x1e", 3);
+      if ((!object->has_no_split_stack()) &&
+           !is_rdssp
+         )
+      {        unsigned char ib[16]={0};
+       if ( view )
+       { ib[0] = *(((unsigned char*)view) + fnoffset);
+         ib[1] = *(((unsigned char*)view) + fnoffset + 1);
+         ib[2] = *(((unsigned char*)view) + fnoffset + 2);
+         ib[3] = *(((unsigned char*)view) + fnoffset + 3);
+       }
        object->error(_("failed to match split-stack sequence at "
-                       "section %u offset %0zx"),
-                     shndx, static_cast<size_t>(fnoffset));
-      return;
+                       "section %u offset %0zx #1:%c #2:%c %u
%2.2hhx.%2.2hhx.%2.2hhx.%2.2hhx"),
+                     shndx, static_cast<size_t>(fnoffset)
+                     , (this->match_view(view, view_size, fnoffset,
+                                         "\x8d\x8c\x24", 3
+                                         ) ? '1' : '0'
+                        )
+                     , (this->match_view(view, view_size, fnoffset,
+                                         "\x8d\x8c\x94", 3
+                                         ) ? '1' : '0'
+                        )
+                      , static_cast<uint32_t>(fnsize)
+                     , ib[0], ib[1], ib[2], ib[3]
+                    );
+      }
+      if ( ! is_rdssp )
+       return;
     }

   // We have to change the function so that it calls
diff -up gold/x86_64.cc~ gold/x86_64.cc
--- gold/x86_64.cc~     2022-01-22 12:14:09.000000000 +0000
+++ gold/x86_64.cc      2022-06-05 18:13:08.085938171 +0100
@@ -6044,10 +6044,12 @@ Target_x86_64<size>::do_ehframe_datarel_
 static const unsigned char cmp_insn_32[] = { 0x64, 0x3b, 0x24, 0x25 };
 static const unsigned char lea_r10_insn_32[] = { 0x44, 0x8d, 0x94, 0x24 };
 static const unsigned char lea_r11_insn_32[] = { 0x44, 0x8d, 0x9c, 0x24 };
+static const unsigned char rdssp_insn_32[]   = { 0xf3, 0x0f, 0x1e, 0xfa };

 static const unsigned char cmp_insn_64[] = { 0x64, 0x48, 0x3b, 0x24, 0x25 };
 static const unsigned char lea_r10_insn_64[] = { 0x4c, 0x8d, 0x94, 0x24 };
 static const unsigned char lea_r11_insn_64[] = { 0x4c, 0x8d, 0x9c, 0x24 };
+static const unsigned char rdssp_insn_64[]   = { 0xf3, 0x0f, 0x1e, 0xfa };

 template<int size>
 void
@@ -6067,7 +6069,9 @@ Target_x86_64<size>::do_calls_non_split(
       (size == 32 ? lea_r10_insn_32 : lea_r10_insn_64);
   const char* const lea_r11_insn = reinterpret_cast<const char*>
       (size == 32 ? lea_r11_insn_32 : lea_r11_insn_64);
-
+  const char* const rdssp_insn = reinterpret_cast<const char*>
+      (size == 32 ? rdssp_insn_32 : rdssp_insn_64);
+  
   const size_t cmp_insn_len =
       (size == 32 ? sizeof(cmp_insn_32) : sizeof(cmp_insn_64));
   const size_t lea_r10_insn_len =
@@ -6075,6 +6079,7 @@ Target_x86_64<size>::do_calls_non_split(
   const size_t lea_r11_insn_len =
       (size == 32 ? sizeof(lea_r11_insn_32) : sizeof(lea_r11_insn_64));
   const size_t nop_len = (size == 32 ? 7 : 8);
+  const size_t rdssp_insn_len = 4;

   // The function starts with a comparison of the stack pointer and a
   // field in the TCB.  This is followed by a jump.
@@ -6108,12 +6113,34 @@ Target_x86_64<size>::do_calls_non_split(
       elfcpp::Swap_unaligned<32, false>::writeval(pval, val);
     }
   else
-    {
-      if (!object->has_no_split_stack())
+    { bool is_rdssp = this->match_view( view, view_size, fnoffset, rdssp_insn,
rdssp_insn_len);
+      if ( (!object->has_no_split_stack())
+         && !is_rdssp
+         )
+      {        unsigned char ib[16]={0};
+       if ( view )
+       { ib[0] = *(((unsigned char*)view) + fnoffset);
+         ib[1] = *(((unsigned char*)view) + fnoffset + 1);
+         ib[2] = *(((unsigned char*)view) + fnoffset + 2);
+         ib[3] = *(((unsigned char*)view) + fnoffset + 3);
+       }
        object->error(_("failed to match split-stack sequence at "
-                       "section %u offset %0zx"),
-                     shndx, static_cast<size_t>(fnoffset));
-      return;
+                       "section %u offset %0zx r10:%c r11:%c %u
%2.2hhx.%2.2hhx.%2.2hhx.%2.2hhx"),
+                     shndx, static_cast<size_t>(fnoffset)
+                     , (this->match_view(view, view_size, fnoffset,
+                                         lea_r10_insn, lea_r10_insn_len
+                                         ) ? '1' : '0'
+                        )
+                     , (this->match_view(view, view_size, fnoffset,
+                                         lea_r11_insn, lea_r11_insn_len
+                                         ) ? '1' : '0'
+                        )
+                      , static_cast<uint32_t>(fnsize)
+                      , ib[0], ib[1], ib[2], ib[3]
+                    );
+      }
+      if( !is_rdssp )
+       return;
     }

   // We have to change the function so that it calls
---END PATCH

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