[Mesa-dev] [PATCH] mesa: fix display list 8-byte alignment issue
Brian Paul
brianp at vmware.com
Tue Jan 27 19:06:07 PST 2015
The _mesa_dlist_alloc() function is only guaranteed to return a pointer
with 4-byte alignment. On 64-bit systems which don't support unaligned
loads (e.g. SPARC or MIPS) this could lead to a bus error in the VBO code.
The solution is to add a new _mesa_dlist_alloc_aligned() function which
will return a pointer to an 8-byte aligned address on 64-bit systems.
This is accomplished by inserting a 4-byte NOP instruction in the display
list when needed.
The only place this actually matters is the VBO code where we need to
allocate a 'struct vbo_save_vertex_list' which needs to be 8-byte
aligned (just as if it were malloc'd).
The gears demo and others hit this bug.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88662
Cc: "10.4" <mesa-stable at lists.freedesktop.org>
---
src/mesa/main/dlist.c | 72 +++++++++++++++++++++++++++++++++++++++++----
src/mesa/main/dlist.h | 3 ++
src/mesa/vbo/vbo_save_api.c | 5 +++-
3 files changed, 73 insertions(+), 7 deletions(-)
diff --git a/src/mesa/main/dlist.c b/src/mesa/main/dlist.c
index 138d360..dc6070b 100644
--- a/src/mesa/main/dlist.c
+++ b/src/mesa/main/dlist.c
@@ -487,6 +487,7 @@ typedef enum
/* The following three are meta instructions */
OPCODE_ERROR, /* raise compiled-in error */
OPCODE_CONTINUE,
+ OPCODE_NOP, /* No-op (used for 8-byte alignment */
OPCODE_END_OF_LIST,
OPCODE_EXT_0
} OpCode;
@@ -1012,13 +1013,16 @@ memdup(const void *src, GLsizei bytes)
* Allocate space for a display list instruction (opcode + payload space).
* \param opcode the instruction opcode (OPCODE_* value)
* \param bytes instruction payload size (not counting opcode)
- * \return pointer to allocated memory (the opcode space)
+ * \param align8 does the payload need to be 8-byte aligned?
+ * This is only relevant in 64-bit environments.
+ * \return pointer to allocated memory (the payload will be at pointer+1)
*/
static Node *
-dlist_alloc(struct gl_context *ctx, OpCode opcode, GLuint bytes)
+dlist_alloc(struct gl_context *ctx, OpCode opcode, GLuint bytes, bool align8)
{
const GLuint numNodes = 1 + (bytes + sizeof(Node) - 1) / sizeof(Node);
const GLuint contNodes = 1 + POINTER_DWORDS; /* size of continue info */
+ GLuint nopNode;
Node *n;
if (opcode < OPCODE_EXT_0) {
@@ -1032,7 +1036,19 @@ dlist_alloc(struct gl_context *ctx, OpCode opcode, GLuint bytes)
}
}
- if (ctx->ListState.CurrentPos + numNodes + contNodes > BLOCK_SIZE) {
+ if (sizeof(void *) == 8 && align8 && ctx->ListState.CurrentPos % 2 == 0) {
+ /* The opcode would get placed at node[0] and the payload would start
+ * at node[1]. But the payload needs to be at an even offset (8-byte
+ * multiple).
+ */
+ nopNode = 1;
+ }
+ else {
+ nopNode = 0;
+ }
+
+ if (ctx->ListState.CurrentPos + nopNode + numNodes + contNodes
+ > BLOCK_SIZE) {
/* This block is full. Allocate a new block and chain to it */
Node *newblock;
n = ctx->ListState.CurrentBlock + ctx->ListState.CurrentPos;
@@ -1042,13 +1058,34 @@ dlist_alloc(struct gl_context *ctx, OpCode opcode, GLuint bytes)
_mesa_error(ctx, GL_OUT_OF_MEMORY, "Building display list");
return NULL;
}
+
+ /* a fresh block should be 8-byte aligned on 64-bit systems */
+ assert(((GLintptr) newblock) % sizeof(void *) == 0);
+
save_pointer(&n[1], newblock);
ctx->ListState.CurrentBlock = newblock;
ctx->ListState.CurrentPos = 0;
+
+ /* Display list nodes are always 4 bytes. If we need 8-byte alignment
+ * we have to insert a NOP so that the payload of the real opcode lands
+ * on an even location:
+ * node[0] = OPCODE_NOP
+ * node[1] = OPCODE_x;
+ * node[2] = start of payload
+ */
+ nopNode = sizeof(void *) == 8 && align8;
}
n = ctx->ListState.CurrentBlock + ctx->ListState.CurrentPos;
- ctx->ListState.CurrentPos += numNodes;
+ if (nopNode) {
+ assert(ctx->ListState.CurrentPos % 2 == 0); /* even value */
+ n[0].opcode = OPCODE_NOP;
+ n++;
+ /* The "real" opcode will now be at an odd location and the payload
+ * will be at an even location.
+ */
+ }
+ ctx->ListState.CurrentPos += nopNode + numNodes;
n[0].opcode = opcode;
@@ -1069,7 +1106,22 @@ dlist_alloc(struct gl_context *ctx, OpCode opcode, GLuint bytes)
void *
_mesa_dlist_alloc(struct gl_context *ctx, GLuint opcode, GLuint bytes)
{
- Node *n = dlist_alloc(ctx, (OpCode) opcode, bytes);
+ Node *n = dlist_alloc(ctx, (OpCode) opcode, bytes, false);
+ if (n)
+ return n + 1; /* return pointer to payload area, after opcode */
+ else
+ return NULL;
+}
+
+
+/**
+ * Same as _mesa_dlist_alloc(), but return a pointer which is 8-byte
+ * aligned in 64-bit environments, 4-byte aligned otherwise.
+ */
+void *
+_mesa_dlist_alloc_aligned(struct gl_context *ctx, GLuint opcode, GLuint bytes)
+{
+ Node *n = dlist_alloc(ctx, (OpCode) opcode, bytes, true);
if (n)
return n + 1; /* return pointer to payload area, after opcode */
else
@@ -1119,7 +1171,7 @@ _mesa_dlist_alloc_opcode(struct gl_context *ctx,
static inline Node *
alloc_instruction(struct gl_context *ctx, OpCode opcode, GLuint nparams)
{
- return dlist_alloc(ctx, opcode, nparams * sizeof(Node));
+ return dlist_alloc(ctx, opcode, nparams * sizeof(Node), false);
}
@@ -8897,6 +8949,9 @@ execute_list(struct gl_context *ctx, GLuint list)
case OPCODE_CONTINUE:
n = (Node *) get_pointer(&n[1]);
break;
+ case OPCODE_NOP:
+ /* no-op */
+ break;
case OPCODE_END_OF_LIST:
done = GL_TRUE;
break;
@@ -9947,6 +10002,9 @@ print_list(struct gl_context *ctx, GLuint list, const char *fname)
fprintf(f, "DISPLAY-LIST-CONTINUE\n");
n = (Node *) get_pointer(&n[1]);
break;
+ case OPCODE_NOP:
+ fprintf(f, "NOP\n");
+ break;
case OPCODE_END_OF_LIST:
fprintf(f, "END-LIST %u\n", list);
done = GL_TRUE;
@@ -10097,6 +10155,8 @@ _mesa_init_display_list(struct gl_context *ctx)
ctx->List.ListBase = 0;
save_vtxfmt_init(&ctx->ListState.ListVtxfmt);
+
+ InstSize[OPCODE_NOP] = 1;
}
diff --git a/src/mesa/main/dlist.h b/src/mesa/main/dlist.h
index c57eb74..6189632 100644
--- a/src/mesa/main/dlist.h
+++ b/src/mesa/main/dlist.h
@@ -60,6 +60,9 @@ extern void _mesa_compile_error( struct gl_context *ctx, GLenum error, const cha
extern void *_mesa_dlist_alloc(struct gl_context *ctx, GLuint opcode, GLuint sz);
+extern void *
+_mesa_dlist_alloc_aligned(struct gl_context *ctx, GLuint opcode, GLuint bytes);
+
extern GLint _mesa_dlist_alloc_opcode( struct gl_context *ctx, GLuint sz,
void (*execute)( struct gl_context *, void * ),
void (*destroy)( struct gl_context *, void * ),
diff --git a/src/mesa/vbo/vbo_save_api.c b/src/mesa/vbo/vbo_save_api.c
index 5055c22..beef342 100644
--- a/src/mesa/vbo/vbo_save_api.c
+++ b/src/mesa/vbo/vbo_save_api.c
@@ -375,11 +375,14 @@ _save_compile_vertex_list(struct gl_context *ctx)
* being compiled.
*/
node = (struct vbo_save_vertex_list *)
- _mesa_dlist_alloc(ctx, save->opcode_vertex_list, sizeof(*node));
+ _mesa_dlist_alloc_aligned(ctx, save->opcode_vertex_list, sizeof(*node));
if (!node)
return;
+ /* Make sure the pointer is aligned to the size of a pointer */
+ assert((GLintptr) node % sizeof(void *) == 0);
+
/* Duplicate our template, increment refcounts to the storage structs:
*/
memcpy(node->attrsz, save->attrsz, sizeof(node->attrsz));
--
1.9.1
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