debug/elf: report size in FormatError for invalid shnum

[cuiweixie]

When e_shnum is 0, the real section count is in sh_size. The FormatError for an invalid value was reporting shnum (always 0) instead of size.

[gopherbot]

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Ian Lance Taylor:

Patch Set 1: Auto-Submit+1 Code-Review+2 Commit-Queue+1

(1 comment)

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[gopherbot]

Message from golang-scoped@luci-project-accounts.iam.gserviceaccount.com:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2026-07-23T04:39:55Z","revision":"c6a768feb6b8b1fae5230863d6a606eb2610dee1"}

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[gopherbot]

Message from Ian Lance Taylor:

Patch Set 1: -Commit-Queue

(Performed by <GERRIT_ACCOUNT_60063> on behalf of <GERRIT_ACCOUNT_5206>)

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[gopherbot]

Message from golang-scoped@luci-project-accounts.iam.gserviceaccount.com:

Patch Set 1:

This CL has failed the run. Reason:

Tryjob golang/try/gotip-linux-arm64 has failed with summary (view all results):

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• go on master (change 804503)

To reproduce, try gomote repro 8675514563851721361.

Additional links for debugging:

• go tool dist test -json output [shard 1]

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Message from golang-scoped@luci-project-accounts.iam.gserviceaccount.com:

Patch Set 1: LUCI-TryBot-Result-1

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