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Custom labels 2 #4

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merged 8 commits into from
Aug 7, 2024
Merged

Custom labels 2 #4

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d30069a
Add "opaquify" hack
umanwizard Aug 1, 2024
38c2ffe
eBPF-side Go custom labels support
umanwizard Aug 1, 2024
c418c23
Usermode-side Go custom labels support
umanwizard Aug 1, 2024
af02c0e
Fix a few lints
umanwizard Aug 1, 2024
c175d91
re-add custom asm
umanwizard Aug 6, 2024
e61559e
fix
umanwizard Aug 6, 2024
5b2b7dc
Use numeric labels instead of named ones
umanwizard Aug 6, 2024
cc821cf
oops...
umanwizard Aug 6, 2024
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39 changes: 34 additions & 5 deletions support/ebpf/interpreter_dispatcher.ebpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -172,6 +172,10 @@ void *get_m_ptr(struct GoCustomLabelsOffsets *offs, UnwindState *state) {

#define MAX_BUCKETS 8

// see https://gcc.gnu.org/onlinedocs/cpp/Stringizing.html#Stringizing
#define STR_HELPER(x) #x
#define STR(x) STR_HELPER(x)

struct GoString {
char *str;
s64 len;
Expand Down Expand Up @@ -311,11 +315,36 @@ bool get_custom_labels(struct pt_regs *ctx, UnwindState *state, GoCustomLabelsOf
DEBUG_PRINT("failed to read custom label: value too long");
continue;
}
if (val_len <= CUSTOM_LABEL_MAX_VAL_LEN)
res = bpf_probe_read(lbl->val.val_bytes, val_len, map_value->values[i].str);
else
res = -1;

// The following assembly statement is equivalent to:
// if (val_len > CUSTOM_LABEL_MAX_VAL_LEN)
// res = bpf_probe_read(lbl->val, val_len, map_value->values[i].str);
// else
// res = -1;
//
// We need to write this in assembly because the verifier doesn't understand
// that val_len has already been bounds-checked above, apparently
// because clang has spilled it to the stack rather than
// keeping it in a register.
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Curious if you tried putting the "register" keyword on val_len?

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I didn't try, but I looked into it and apparently modern compilers simply ignore the register keyword: https://stackoverflow.com/questions/10675072/is-the-register-keyword-still-used


// clang-format off
asm volatile(
// Note: this branch is never taken, but we
// need it to appease the verifier.
"if %2 > " STR(CUSTOM_LABEL_MAX_VAL_LEN) " goto bad%=\n"
"r1 = %1\n"
"r2 = %2\n"
"r3 = %3\n"
"call 4\n"
"%0 = r0\n"
"goto good%=\n"
"bad%=: %0 = -1\n"
"good%=:\n"
: "=r"(res)
: "r"(lbl->val), "r"(val_len), "r"(map_value->values[i].str)
// all r0-r5 are clobbered since we make a function call.
: "r0", "r1", "r2", "r3", "r4", "r5", "memory"
);
// clang-format on
if (res) {
DEBUG_PRINT("failed to read value for custom label: %ld", res);
continue;
Expand Down