Fix memory leaks from mono_type_full_name in marshal-shared.c error paths

[Copilot]

mono_type_full_name() returns a heap-allocated string, but several call sites in marshal-shared.c passed the result directly into g_strdup_printf without freeing it — leaking on every hit. These paths can fire repeatedly during AOT compilation against assemblies with many invalid marshal configurations.

Description

Store each mono_type_full_name() result in a local, use it, then g_free it:

// Before
char *msg = g_strdup_printf("Type %s ...", mono_type_full_name(m_class_get_byval_arg(klass)));

// After
char *type_name = mono_type_full_name(m_class_get_byval_arg(klass));
char *msg = g_strdup_printf("Type %s ...", type_name);
g_free(type_name);

Fixed sites:

• Auto-layout check — g_strdup_printf with single mono_type_full_name; result stored, used, and freed
• Explicit-layout g_error path — left as-is (inline mono_type_full_name call); g_error is fatal and never returns, and in DISABLE_ASSERT_MESSAGES builds its variadic args are discarded entirely — introducing a local variable causes an unused-variable build error in WASM/WASI configurations
• Generic type marshal check — g_strdup_printf with single mono_type_full_name; result stored, used, and freed
• Struct field type check — g_strdup_printf with two mono_type_full_name calls; both results stored, used, and freed

Customer Impact

Cumulative memory growth during AOT compilation of assemblies containing types with invalid marshal configurations (auto-layout structs, non-blittable generic fields, reference-typed struct fields).

Regression

No — pre-existing leak, not a regression.

Testing

Validated by code inspection and CI. These are error paths with no dedicated test infrastructure in the repo; the fix is mechanical and low-risk.

Risk

Very low. Changes are confined to error paths that emit a marshal exception. No logic changes — only introduction of local variables and paired g_free calls before strings go out of scope. The g_error path is intentionally left unchanged to avoid a -Werror,-Wunused-variable build failure in WASM/WASI configurations where g_error discards its variadic arguments.

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Original prompt

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This section details on the original issue you should resolve

<issue_title>Memory leaks from mono_type_full_name in marshal-shared.c error paths</issue_title>
<issue_description>## Description

mono_type_full_name() returns an allocated string, but several call sites in src/mono/mono/metadata/marshal-shared.c pass it directly into g_strdup_printf or g_error without freeing the intermediate allocation:

• Line 778: g_strdup_printf("Type %s ...", mono_type_full_name(...))
• Line 816: g_error("Type %s ...", mono_type_full_name(...))
• Line 866: g_strdup_printf("Generic type %s ...", mono_type_full_name(...))
• Lines 912-913: g_strdup_printf("Type %s with field type %s ...", mono_type_full_name(...), mono_type_full_name(...))

Each leaks the string returned by mono_type_full_name(). While these are error paths, they can fire repeatedly during AOT compilation (e.g., when processing assemblies with many invalid marshal configurations), causing cumulative memory growth.

Fix

Store the result in a temporary, use it in the format string, then g_free it:

char *type_name = mono_type_full_name(m_class_get_byval_arg(klass));
char *msg = g_strdup_printf("Type %s ...", type_name);
g_free(type_name);
mono_marshal_shared_mb_emit_exception_marshal_directive(mb, msg);

This pattern should be applied to all call sites in the file.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Memory leaks from mono_type_full_name in marshal-shared.c error paths #125576

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[lewing]

@copilot take a look at the failures

[Copilot]

@copilot take a look at the failures

The build was failing with unused variable 'type_name' [-Werror,-Wunused-variable] in WASM/WASI builds (commit 3ef96fb).

Root cause: when DISABLE_ASSERT_MESSAGES is defined (used in WASM/WASI builds), g_error(...) expands to g_log_disabled(domain, level, file, line); eg_unreachable() — the variadic arguments are discarded entirely, so the local type_name variable was never actually used.

Fixed in commit 56129333: reverted the g_error call site back to the original inline mono_type_full_name() form. Since g_error is fatal and aborts the process, the transient memory leak is irrelevant. The other three g_strdup_printf sites (the real leaks) remain fixed.

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[Copilot]

Pull request overview

Fixes repeated heap leaks in Mono marshaling error paths by ensuring mono_type_full_name() results are freed after being used to format exception messages during IL generation (notably during AOT compilation when many invalid marshal configurations are encountered).

Changes:

• Store mono_type_full_name(...) results into locals before g_strdup_printf(...) and g_free(...) them afterward.
• Apply the pattern to the auto-layout struct check, non-blittable generic field check, and struct field type check (two type-name allocations).

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