On Mon, 2023-11-20 at 16:22 -0800, Andrii Nakryiko wrote:
[...]
> +SEC("raw_tp")
> +__log_level(2)
> +__success
> +__naked void partial_stack_load_preserves_zeros(void)
> +{
> + asm volatile (
> + /* fp-8 is all STACK_ZERO */
> + "*(u64 *)(r10 -8) = 0;"
This fails when compiled with llvm-16, bpf st assembly support is only
present in llvm-18. If we want to preserve support for llvm-16 this
test would require ifdefs or the following patch:
@@ -3,6 +3,7 @@
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
+#include "../../../include/linux/filter.h"
#include "bpf_misc.h"
struct {
@@ -510,7 +511,7 @@ __naked void partial_stack_load_preserves_zeros(void)
{
asm volatile (
/* fp-8 is all STACK_ZERO */
- "*(u64 *)(r10 -8) = 0;"
+ ".8byte %[fp8_st_zero];"
/* fp-16 is const zero register */
"r0 = 0;"
@@ -559,7 +560,8 @@ __naked void partial_stack_load_preserves_zeros(void)
"r0 = 0;"
"exit;"
:
- : __imm_ptr(single_byte_buf)
+ : __imm_ptr(single_byte_buf),
+ __imm_insn(fp8_st_zero, BPF_ST_MEM(BPF_DW, BPF_REG_FP, -8, 0))
: __clobber_common);
}
> + /* fp-16 is const zero register */
> + "r0 = 0;"
> + "*(u64 *)(r10 -16) = r0;"
> +
> + /* load single U8 from non-aligned STACK_ZERO slot */
> + "r1 = %[single_byte_buf];"
> + "r2 = *(u8 *)(r10 -1);"
> + "r1 += r2;" /* this should be fine */
Question: the comment suggests that adding something other than
zero would be an error, however error would only be
reported if *r1 is attempted, maybe add such access?
E.g. "*(u8 *)(r1 + 0) = r2;"?
[...]
