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[LLD][Docs] Document -z gcs= option in the man page #146522

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MarkMurrayARM merged 5 commits into from
Jul 21, 2025
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[LLD][Docs] Document -z gcs= option in the man page #146522

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[LLD][Docs] Document `-z gcs` option in the man page
sivan-shani Jul 1, 2025
fb65d4d
[LLD][Docs] Document -z gcs= option in the man page
sivan-shani Jul 1, 2025
0129664
[LLD][Docs] Improve wording and clarity in response to review comments
sivan-shani Jul 2, 2025
68b2552
[LLD][Docs] Align indication of 'default' option, respnd to review co…
sivan-shani Jul 2, 2025
9640c1f
[LLD][Docs] Add .Cm, use 'relocatable files' respond to review comments.
sivan-shani Jul 3, 2025
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[LLD][Docs] Document -z gcs option in the man page 
Add documentation for the `-z gcs` option to the LLD man page. This flag controls how the GCS bit is set in the output:

- implicit (default): inferred from input objects
- never: GCS bit is never set
- always: GCS bit is always set

Clarifies behavior for users and aligns the man page with existing functionality.
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sivan-shani committed Jul 1, 2025
commit cce8b24fc4fab4e4614e0f641180cf7b9146e499
10 changes: 10 additions & 0 deletions lld/docs/ld.lld.1
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Expand Up @@ -953,6 +953,16 @@ disallows overlap.
.It Cm shstk
x86 only, use shadow stack.
.Pp
.It Cm gcs Ns = Ns Ar [implicit|never|always]
Specify how the GCS bit is set. Set GCS bit indicates object file that supports Guarded Control Stack.
Specify how the GCS bit is set. A set GCS bit indicates that the object file supports the Guarded Control Stack security feature.
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@smithp35 smithp35 Jul 1, 2025

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I think it would be better to say

Specify how the GNU_PROPERTY_AARCH64_FEATURE_1_GCS feature bit is set in the output ELF file. When set this declares that the ELF file supports the Guarded Control Stack (GCS) security feature.

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@sivan-shani sivan-shani Jul 2, 2025

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ack, wording improved

.Cm implicit
is the default, where the GCS bit is inferred from the input objects.
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@smithp35 smithp35 Jul 1, 2025

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From looking at noseparate-code above. I suggest
(default) feature bit is inferred from the input object marking.

I've suggested feature bit rather than GCS bit as we've used the full GNU_PROPERTY_AARCH64_FEATURE_1_GCS feature bit above.

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@sivan-shani sivan-shani Jul 2, 2025

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ack, wording improved

.Cm never
disables the GCS bit regardless of input markings.
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@smithp35 smithp35 Jul 1, 2025

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I suggest
clears the feature bit regardless of input object marking.

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@sivan-shani sivan-shani Jul 2, 2025

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ack, wording improved

.Cm always
enables the GCS bit regardless of input markings.
.Pp
.It Cm stack-size Ns = Ns Ar size
Set the main thread's stack size to
.Ar size .
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