chore(blazesym): bump to v0.2.4, drop pure-Go kallsyms fallback

[dpsoft]

What

Bumps blazesym to v0.2.4 and removes the pure-Go /proc/kallsyms kernel-symbolization fallback that was added in #25 as a workaround for older blazesym.

Why

#25 added a pure-Go kallsyms fallback because pre-0.2.4 blazesym hard-failed kernel symbolization with BLAZE_ERR_PERMISSION_DENIED whenever /proc/kcore was inaccessible (lockdown=integrity / Secure Boot / no CAP_SYS_RAWIO).

blazesym v0.2.4 (987d36c, "kernel: Don't require /proc/kcore access when only kallsyms is used") fixes the root cause: it only reads /proc/kcore for the KASLR offset when a vmlinux DWARF resolver is actually present. On the common production host (no /boot/vmlinux-* DWARF installed) blazesym resolves kallsyms-only without ever touching kcore, returning the same name+offset the pure-Go fallback gave — so ~1100 lines of fallback machinery are now redundant.

Verification

Tested on a real lockdown=integrity host (kcore 0400, binary setcap'd without cap_sys_rawio, no /boot/vmlinux DWARF):

symbolize: batches=372 input_ips=2763 batch_failures=0 raw_addr_frames=0 eperm=0 other_err=0

eperm=0, fallback_engaged=0, kernel frames fully named (do_syscall_64, __schedule, finish_task_switch, __d_lookup, …).

• make build links clean against v0.2.4
• unit tests pass (incl. changed CGO pkgs: symbolize, perfagent, pprof, debuginfod, debuginfod/cache)
• integration suite: 40 pass / 0 fail / 1 skip — TestKernelStackResolution (the test exercising this change) passes; the lone skip is TestOffBoxLibcResolution, unsatisfiable here because glibc-debuginfo isn't published for fc44

Changes

• remove symbolize/{kallsyms,kallsyms_cache}.go and their tests (pure-Go symbolizer + disk cache + boot-id EPERM marker)
• simplify symbolize/local_kernel.go: SymbolizeKernel calls blazesym directly; on any error it preserves raw kernel addresses (rawKernelAddrFrames) so kernel context still survives into the pprof
• drop the now-meaningless KernelFallbackEngaged counter from stats + the /metrics endpoint (keep KernelLockdownEPERM / KernelOtherErr for observability)
• remove PERFAGENT_FORCE_KERNEL_FALLBACK env + the forced-fallback integration test
• regenerate eBPF bytecode (.o)

Notes

Pinned to the v0.2.4 tag (the local go.mod uses a path replace, so the bump is just the blazesym checkout). The only case v0.2.4 doesn't cover — /boot/vmlinux-* DWARF installed and lockdown — is handled by post-v0.2.4 _stext KASLR fallback on blazesym main; it's a self-contradictory combo in practice (you don't ship debug vmlinux to a Secure Boot box), and the kept rawKernelAddrFrames backstop degrades it gracefully to raw addresses regardless.

[Copilot]

Pull request overview

This PR updates the kernel symbolization pipeline to rely on blazesym v0.2.4 behavior (no longer requiring /proc/kcore for kallsyms-only resolution in the common case) and removes the now-redundant pure-Go /proc/kallsyms fallback machinery and its observability surface area.

Changes:

• Remove the pure-Go kallsyms symbolizer + disk cache + EPERM marker logic and simplify LocalKernelSymbolizer to call blazesym directly, falling back only to raw-address frames on error.
• Remove the forced-fallback integration test and the KernelFallbackEngaged counter/metric, updating metrics output and unit tests accordingly.
• Update related documentation/comments and schemas to reflect the new “blazesym-only + raw-addr backstop” model.

Reviewed changes

Copilot reviewed 16 out of 26 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
symbolize/local_kernel.go	Removes the fallback ladder and makes kernel symbolization blazesym-only with raw-address backstop on any blazesym error.
symbolize/stats.go	Drops KernelFallbackEngaged and updates counter semantics/comments for the simplified flow.
symbolize/stats_test.go	Updates stats tests and adds a seam-based stub to exercise raw-address backstop/stats without CGO.
perfagent/metrics_endpoint.go	Removes the perf_agent_symbolize_kernel_fallback_engaged metric and updates HELP text for remaining metrics.
perfagent/metrics_endpoint_test.go	Updates Prometheus exposition expectations after metric removal.
test/integration_test.go	Removes the forced-fallback integration test that depended on the deleted fallback behavior.
symbolize/allocs_budget_test.go	Removes allocation-budget tests that were specific to the deleted kallsyms parser/resolver.
bench/internal/schema/schema.go	Updates self-metrics commentary to reflect “blazesym broke” rather than “blazesym + fallback broke”.
symbolize/kallsyms.go (deleted)	Removes pure-Go /proc/kallsyms symbolizer implementation.
symbolize/kallsyms_cache.go (deleted)	Removes kallsyms disk cache + boot-id/EPERM marker logic.
symbolize/kallsyms_*test.go (deleted)	Removes unit/bench tests for deleted kallsyms parser/cache/symbolizer.
symbolize/local_kernel_fallback_test.go (deleted)	Removes tests that pinned the old fallback ladder behavior.
symbolize/blazesym_eperm_marker_test.go (deleted)	Removes tests for the deleted EPERM marker mechanism.

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