[Mesa-dev] [PATCH] mapi: fix LTO compilation

[Jan Ziak (⚛)]

LTO compilation can sometimes fail with GCC 4.9 and GCC 5.3 because
src/mapi uses unusual mixing of C code and assembly code. The issue
may be present in case of GCC 6.1 as well.

This is a Mesa bug rather than a compiler bug (although in an ideal
world the compilation with -flto should fail if and only if normal
compilation fails).

The error message:

entry_x86-64_tls.h:61: undefined reference to `x86_64_entry_start'

Without the patch:
- using "-flto -O2 -DDEBUG" fails with GCC 4.9 and 5.3
- using "-flto -O3 -DDEBUG" succeeds with GCC 4.9 and 5.3
- using "-flto -O2 -DNDEBUG" succeeds with GCC 4.9 and 5.3

The patch assumes that the assembler understands ".hidden" directive.

Signed-off-by: Jan Ziak (⚛) <0xe2.0x9a.0x9b at gmail.com>
---
 src/mapi/entry_x86-64_tls.h |  5 +++--
 src/mapi/entry_x86_tls.h    | 12 +++++++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/mapi/entry_x86-64_tls.h b/src/mapi/entry_x86-64_tls.h
index 38faccc..acabecc 100644
--- a/src/mapi/entry_x86-64_tls.h
+++ b/src/mapi/entry_x86-64_tls.h
@@ -28,6 +28,8 @@
 
 __asm__(".text\n"
         ".balign 32\n"
+        ".globl x86_64_entry_start\n"
+        ".hidden x86_64_entry_start\n"
         "x86_64_entry_start:");
 
 #define STUB_ASM_ENTRY(func)                             \
@@ -54,8 +56,7 @@ entry_patch_public(void)
 {
 }
 
-static char
-x86_64_entry_start[];
+extern char x86_64_entry_start[];
 
 mapi_func
 entry_get_public(int slot)
diff --git a/src/mapi/entry_x86_tls.h b/src/mapi/entry_x86_tls.h
index 46d2ece..6078b9a 100644
--- a/src/mapi/entry_x86_tls.h
+++ b/src/mapi/entry_x86_tls.h
@@ -29,7 +29,9 @@
 
 __asm__(".text");
 
-__asm__("x86_current_tls:\n\t"
+__asm__( ".globl x86_current_tls\n"
+	".hidden x86_current_tls\n"
+	"x86_current_tls:\n\t"
 	"call 1f\n"
         "1:\n\t"
         "popl %eax\n\t"
@@ -42,6 +44,8 @@ __asm__(".section wtext, \"awx\", @progbits");
 #endif /* GLX_X86_READONLY_TEXT */
 
 __asm__(".balign 16\n"
+        ".globl x86_entry_start\n"
+        ".hidden x86_entry_start\n"
         "x86_entry_start:");
 
 #define STUB_ASM_ENTRY(func)     \
@@ -60,6 +64,8 @@ __asm__(".balign 16\n"
 
 #ifndef GLX_X86_READONLY_TEXT
 __asm__(".balign 16\n"
+        ".globl x86_entry_end\n"
+        ".hidden x86_entry_end\n"
         "x86_entry_end:");
 __asm__(".text");
 #endif /* GLX_X86_READONLY_TEXT */
@@ -71,8 +77,8 @@ __asm__(".text");
 extern unsigned long
 x86_current_tls();
 
-static char x86_entry_start[];
-static char x86_entry_end[];
+extern char x86_entry_start[];
+extern char x86_entry_end[];
 
 void
 entry_patch_public(void)
-- 
2.8.3