From: Abhishek Dubey <[email protected]>
Move the long branch address field to the bottom of the long
branch stub. This allows uninterrupted disassembly until the
last 4/8 bytes. The last bytes exclusion is logically necessary to
prevent disassembly failure, otherwise the actual program layout
is never altered. Hence no effect on overall program size.
Also, align dummy_tramp_addr field with 8-byte boundary.
Following is disassembler output for test program with moved down
dummy_tramp_addr field:
.....
.....
pc:68 left:44 a6 03 08 7c : mtlr 0
pc:72 left:40 bc ff ff 4b : b .-68
pc:76 left:36 a6 02 68 7d : mflr 11
pc:80 left:32 05 00 9f 42 : bcl 20, 31, .+4
pc:84 left:28 a6 02 88 7d : mflr 12
pc:88 left:24 14 00 8c e9 : ld 12, 20(12)
pc:92 left:20 a6 03 89 7d : mtctr 12
pc:96 left:16 a6 03 68 7d : mtlr 11
pc:100 left:12 20 04 80 4e : bctr
pc:104 left:8 c0 34 1d 00 :
Failure log:
Can't disasm instruction at offset 104: c0 34 1d 00 00 00 00 c0
Disassembly logic can truncate at 104, ignoring last 8 bytes.
Update the dummy_tramp_addr field offset calculation from the end
of the program to reflect its new location, for bpf_arch_text_poke()
to update the actual trampoline's address in this field.
All BPF trampoline selftests continue to pass with this patch applied.
Fixes: d243b62b7bd3 ("powerpc64/bpf: Add support for bpf trampolines")
Signed-off-by: Abhishek Dubey <[email protected]>
Signed-off-by: Saket Kumar Bhaskar <[email protected]>
Tested-by: Yeswanth Krishna Tellakula <[email protected]>
---
arch/powerpc/net/bpf_jit_comp.c | 46 +++++++++++++++++----------------
1 file changed, 24 insertions(+), 22 deletions(-)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index f2e0f9755e65..bdae835e4b71 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -52,9 +52,10 @@ asm (
void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct
codegen_context *ctx)
{
int ool_stub_idx, long_branch_stub_idx;
- int ool_stub_sz;
+ int stub_sz;
/*
+ * The dummy_tramp_addr field is placed at bottom of Long branch stub.
* In the final pass, align the mis-aligned dummy_tramp_addr field
* in the fimage. The alignment NOP must appear before OOL stub,
* to make ool_stub_idx & long_branch_stub_idx constant from end.
@@ -62,13 +63,10 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage,
struct codegen_context
* dummy_tramp_addr must be 8-byte aligned for load-register
* compatibility. The fimage can be non 8-byte aligned, so final
* alignment depends on start of fimage and the stub's instruction
- * count offset. The OOL stub size is 4 instructions (with
- * CONFIG_PPC_FTRACE_OUT_OF_LINE) or 3 instructions (without)
- * before dummy_tramp_addr.
- *
- * Emit a NOP here if (ctx->idx + ool_stub_sz) is odd, so that
- * dummy_tramp_addr lands at an even instruction offset (== 8-byte
- * aligned from an 8-byte aligned base).
+ * count. The stubs block has 11 instructions (with
+ * CONFIG_PPC_FTRACE_OUT_OF_LINE) or 10 instructions (without)
+ * before dummy_tramp_addr field. Emit a NOP if the address of
+ * dummy_tramp_addr is non aligned.
*
* In pass=0 when image==NULL, conservatively account for space
* required to accommodate alignment NOP. In case final pass skips
@@ -76,8 +74,8 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage,
struct codegen_context
* jited_len signifies correct program size.
*/
- ool_stub_sz = IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 16 : 12;
- if (!image || !IS_ALIGNED((unsigned long)fimage + ctx->idx*4 +
ool_stub_sz, SZL))
+ stub_sz = IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 44 : 40;
+ if (!image || !IS_ALIGNED((unsigned long)fimage + ctx->idx*4 + stub_sz,
SZL))
EMIT(PPC_RAW_NOP());
/*
@@ -98,28 +96,29 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage,
struct codegen_context
/*
* Long branch stub:
- * .long <dummy_tramp_addr> // 8-byte aligned
* mflr r11
* bcl 20,31,$+4
- * mflr r12
- * ld r12, -8-SZL(r12)
+ * mflr r12 // lr/r12 stores pc of current(this) inst.
+ * ld r12, 20(r12) // offset(dummy_tramp_addr) from prev
inst. is 20
* mtctr r12
- * mtlr r11 // needed to retain ftrace ABI
+ * mtlr r11 // needed to retain ftrace ABI
* bctr
+ * .long <dummy_tramp_addr> // SZL bytes aligned
*/
- if (image)
- *((unsigned long *)&image[ctx->idx]) = (unsigned
long)dummy_tramp;
-
- ctx->idx += SZL / 4;
long_branch_stub_idx = ctx->idx;
EMIT(PPC_RAW_MFLR(_R11));
EMIT(PPC_RAW_BCL4());
EMIT(PPC_RAW_MFLR(_R12));
- EMIT(PPC_RAW_LL(_R12, _R12, -8-SZL));
+ EMIT(PPC_RAW_LL(_R12, _R12, 20));
EMIT(PPC_RAW_MTCTR(_R12));
EMIT(PPC_RAW_MTLR(_R11));
EMIT(PPC_RAW_BCTR());
+ if (image)
+ *((unsigned long *)&image[ctx->idx]) = (unsigned
long)dummy_tramp;
+
+ ctx->idx += SZL / 4;
+
if (!bpf_jit_ool_stub) {
bpf_jit_ool_stub = (ctx->idx - ool_stub_idx) * 4;
bpf_jit_long_branch_stub = (ctx->idx - long_branch_stub_idx) *
4;
@@ -1295,6 +1294,7 @@ static void do_isync(void *info __maybe_unused)
* bpf_func:
* [nop|b] ool_stub
* 2. Out-of-line stub:
+ * nop // optional nop for alignment
* ool_stub:
* mflr r0
* [b|bl] <bpf_prog>/<long_branch_stub>
@@ -1302,14 +1302,14 @@ static void do_isync(void *info __maybe_unused)
* b bpf_func + 4
* 3. Long branch stub:
* long_branch_stub:
- * .long <branch_addr>/<dummy_tramp>
* mflr r11
* bcl 20,31,$+4
* mflr r12
- * ld r12, -16(r12)
+ * ld r12, 20(r12)
* mtctr r12
* mtlr r11 // needed to retain ftrace ABI
* bctr
+ * .long <branch_addr>/<dummy_tramp>
*
* dummy_tramp is used to reduce synchronization requirements.
*
@@ -1411,10 +1411,12 @@ int bpf_arch_text_poke(void *ip, enum
bpf_text_poke_type old_t,
* 1. Update the address in the long branch stub:
* If new_addr is out of range, we will have to use the long branch
stub, so patch new_addr
* here. Otherwise, revert to dummy_tramp, but only if we had patched
old_addr here.
+ *
+ * dummy_tramp_addr moved to bottom of long branch stub.
*/
if ((new_addr && !is_offset_in_branch_range(new_addr - ip)) ||
(old_addr && !is_offset_in_branch_range(old_addr - ip)))
- ret = patch_ulong((void *)(bpf_func_end -
bpf_jit_long_branch_stub - SZL),
+ ret = patch_ulong((void *)(bpf_func_end - SZL), /* SZL:
dummy_tramp_addr offset */
(new_addr &&
!is_offset_in_branch_range(new_addr - ip)) ?
(unsigned long)new_addr : (unsigned
long)dummy_tramp);
if (ret)
--
2.54.0
