[PATCH 1/2] powerpc: Link VDSOs at 0x0

[PATCH 1/2] powerpc: Link VDSOs at 0x0

[Anton Blanchard]

perf is failing to resolve symbols in the VDSO. A while (1)
gettimeofday() loop shows:

93.99%  [vdso]  [.] 0x00000000000005e0
 3.12%  test    [.] 00000037.plt_call.gettimeofday@@GLIBC_2.18
 2.81%  test    [.] main

The reason for this is that we are linking our VDSO shared libraries
at 1MB, which is a little weird. Even though this is uncommon, Alan
points out that it is valid and we should probably fix perf userspace.

Regardless, I can't see a reason why we are doing this. The code
is all position independent and we never rely on the VDSO ending
up at 1M (and we never place it there on 64bit tasks).

Changing our link address to 0x0 fixes perf VDSO symbol resolution:

73.18%  [vdso]  [.] 0x000000000000060c
12.39%  [vdso]  [.] __kernel_gettimeofday
 3.58%  test    [.] 00000037.plt_call.gettimeofday@@GLIBC_2.18
 2.94%  [vdso]  [.] __kernel_datapage_offset
 2.90%  test    [.] main

We still have some local symbol resolution issues that will be
fixed in a subsequent patch.

Signed-off-by: Anton Blanchard <anton@samba.org>
---

diff --git a/arch/powerpc/include/asm/vdso.h b/arch/powerpc/include/asm/vdso.h
index 0d9cecd..c53f5f6 100644
--- a/arch/powerpc/include/asm/vdso.h
+++ b/arch/powerpc/include/asm/vdso.h
@@ -4,11 +4,11 @@
 #ifdef __KERNEL__
 
 /* Default link addresses for the vDSOs */
-#define VDSO32_LBASE	0x100000
-#define VDSO64_LBASE	0x100000
+#define VDSO32_LBASE	0x0
+#define VDSO64_LBASE	0x0
 
 /* Default map addresses for 32bit vDSO */
-#define VDSO32_MBASE	VDSO32_LBASE
+#define VDSO32_MBASE	0x100000
 
 #define VDSO_VERSION_STRING	LINUX_2.6.15
 

[PATCH 2/2] powerpc: Use unstripped VDSO image for more accurate profiling data

[Anton Blanchard]

We are seeing a lot of hits in the VDSO that are not resolved by perf.
A while(1) gettimeofday() loop shows the issue:

27.64%  [vdso]  [.] 0x000000000000060c                        
22.57%  [vdso]  [.] 0x0000000000000628                        
16.88%  [vdso]  [.] 0x0000000000000610                        
12.39%  [vdso]  [.] __kernel_gettimeofday                     
 6.09%  [vdso]  [.] 0x00000000000005f8                        
 3.58%  test    [.] 00000037.plt_call.gettimeofday@@GLIBC_2.18
 2.94%  [vdso]  [.] __kernel_datapage_offset                  
 2.90%  test    [.] main                                      

We are using a stripped VDSO image which means only symbols with
relocation info can be resolved. There isn't a lot of point to
stripping the VDSO, the debug info is only about 1kB:

4680 arch/powerpc/kernel/vdso64/vdso64.so
5815 arch/powerpc/kernel/vdso64/vdso64.so.dbg

By using the unstripped image, we can resolve all the symbols in the
VDSO and the perf profile data looks much better:

76.53%  [vdso]  [.] __do_get_tspec                            
12.20%  [vdso]  [.] __kernel_gettimeofday                     
 5.05%  [vdso]  [.] __get_datapage                            
 3.20%  test    [.] main                                      
 2.92%  test    [.] 00000037.plt_call.gettimeofday@@GLIBC_2.18

Signed-off-by: Anton Blanchard <anton@samba.org>
---

diff --git a/arch/powerpc/kernel/vdso32/vdso32_wrapper.S b/arch/powerpc/kernel/vdso32/vdso32_wrapper.S
index 6e8f507..37e2e13 100644
--- a/arch/powerpc/kernel/vdso32/vdso32_wrapper.S
+++ b/arch/powerpc/kernel/vdso32/vdso32_wrapper.S
@@ -7,7 +7,7 @@
 	.globl vdso32_start, vdso32_end
 	.balign PAGE_SIZE
 vdso32_start:
-	.incbin "arch/powerpc/kernel/vdso32/vdso32.so"
+	.incbin "arch/powerpc/kernel/vdso32/vdso32.so.dbg"
 	.balign PAGE_SIZE
 vdso32_end:
 
diff --git a/arch/powerpc/kernel/vdso64/vdso64_wrapper.S b/arch/powerpc/kernel/vdso64/vdso64_wrapper.S
index b8553d6..01e7799 100644
--- a/arch/powerpc/kernel/vdso64/vdso64_wrapper.S
+++ b/arch/powerpc/kernel/vdso64/vdso64_wrapper.S
@@ -7,7 +7,7 @@
 	.globl vdso64_start, vdso64_end
 	.balign PAGE_SIZE
 vdso64_start:
-	.incbin "arch/powerpc/kernel/vdso64/vdso64.so"
+	.incbin "arch/powerpc/kernel/vdso64/vdso64.so.dbg"
 	.balign PAGE_SIZE
 vdso64_end: