[PATCH v3 2/5] pcm_dmix assembly: fix the interface for safety

[frederic.recoules at univ-grenoble-alpes.fr]

From: Frédéric Recoules <frederic.recoules at orange.fr>

- move 'size' and 'old_ebx' in the output section
  since they are clobbered;
- add the "memory" clobber since input pointers
  are accessed;
- (minor) add the "cc" clobber since flags are
  clobbered.

  The compiler is missing some dataflow information
  about the execution of the assembly chunks.
  For instance, it assumes that 'size' remains unchanged
  and that no input pointer is accessed.
  The compiler optimizer may take advantage of these
  assumption and produce a wrong code.

Note: currently produces the same binary output.

Signed-off-by: Frédéric Recoules <frederic.recoules at orange.fr>
---
 src/pcm/pcm_dmix_i386.h   | 45 +++++++++++++++++----------------------
 src/pcm/pcm_dmix_x86_64.h | 27 +++++++++++------------
 2 files changed, 32 insertions(+), 40 deletions(-)

diff --git a/src/pcm/pcm_dmix_i386.h b/src/pcm/pcm_dmix_i386.h
index e816d5e0..3ea0737d 100644
--- a/src/pcm/pcm_dmix_i386.h
+++ b/src/pcm/pcm_dmix_i386.h
@@ -142,12 +142,11 @@ static void MIX_AREAS_16(unsigned int size,
 		"7:"
 		"\tmovl %[old_ebx], %%ebx\n"	/* ebx is GOT pointer (-fPIC) */
 
-		: /* no output regs */
-		: [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+		: [size] "+m" (size), [old_ebx] "=m" (old_ebx)
+		: [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_ebx] "m" (old_ebx)
-		: "esi", "edi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "esi", "edi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
 
@@ -233,12 +232,11 @@ static void MIX_AREAS_16_MMX(unsigned int size,
                 "5:"
 		"\tmovl %[old_ebx], %%ebx\n"	/* ebx is GOT pointer (-fPIC) */
 
-		: /* no output regs */
-		: [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+	        : [size] "+m" (size), [old_ebx] "=m" (old_ebx)
+		: [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_ebx] "m" (old_ebx)
-		: "esi", "edi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "esi", "edi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
 
@@ -347,12 +345,11 @@ static void MIX_AREAS_32(unsigned int size,
 		"6:"
 		"\tmovl %[old_ebx], %%ebx\n"	/* ebx is GOT pointer (-fPIC) */
 
-		: /* no output regs */
-		: [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+		: [size] "+m" (size), [old_ebx] "=m" (old_ebx)
+		: [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_ebx] "m" (old_ebx)
-		: "esi", "edi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "esi", "edi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
 
@@ -454,12 +451,11 @@ static void MIX_AREAS_24(unsigned int size,
 		"6:"
 		"\tmovl %[old_ebx], %%ebx\n"	/* ebx is GOT pointer (-fPIC) */
 
-		: /* no output regs */
-		: [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+	        : [size] "+m" (size), [old_ebx] "=m" (old_ebx)
+		: [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_ebx] "m" (old_ebx)
-		: "esi", "edi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "esi", "edi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
 
@@ -554,11 +550,10 @@ static void MIX_AREAS_24_CMOV(unsigned int size,
 		"6:"
 		"\tmovl %[old_ebx], %%ebx\n"	/* ebx is GOT pointer (-fPIC) */
 
-		: /* no output regs */
-		: [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+	        : [size] "+m" (size), [old_ebx] "=m" (old_ebx)
+		: [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_ebx] "m" (old_ebx)
-		: "esi", "edi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "esi", "edi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
diff --git a/src/pcm/pcm_dmix_x86_64.h b/src/pcm/pcm_dmix_x86_64.h
index dc433b35..7f711547 100644
--- a/src/pcm/pcm_dmix_x86_64.h
+++ b/src/pcm/pcm_dmix_x86_64.h
@@ -114,12 +114,11 @@ static void MIX_AREAS_16(unsigned int size,
 		"\temms\n"
 		"\tmovq %[old_rbx], %%rbx\n"
 
-		: /* no output regs */
-	        : [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+		: [size] "+m" (size), [old_rbx] "=m" (old_rbx)
+	        : [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_rbx] "m" (old_rbx)
-		: "rsi", "rdi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "rsi", "rdi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
 
@@ -230,12 +229,11 @@ static void MIX_AREAS_32(unsigned int size,
 		"6:"
 		"\tmovq %[old_rbx], %%rbx\n"
 
-		: /* no output regs */
-	        : [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+		: [size] "+m" (size), [old_rbx] "=m" (old_rbx)
+	        : [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_rbx] "m" (old_rbx)
-		: "rsi", "rdi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "rsi", "rdi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
 
@@ -334,11 +332,10 @@ static void MIX_AREAS_24(unsigned int size,
 		"6:"
 		"\tmovq %[old_rbx], %%rbx\n"
 
-		: /* no output regs */
-	        : [size] "m" (size),
-		  [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
+		: [size] "+m" (size), [old_rbx] "=m" (old_rbx)
+	        : [dst] "m" (dst), [src] "m" (src), [sum] "m" (sum),
 		  [dst_step] "m" (dst_step),  [src_step] "m" (src_step),
-		  [sum_step] "m" (sum_step), [old_rbx] "m" (old_rbx)
-		: "rsi", "rdi", "edx", "ecx", "eax"
+		  [sum_step] "m" (sum_step)
+		: "rsi", "rdi", "edx", "ecx", "eax", "memory", "cc"
 	);
 }
-- 
2.17.1