MAIN_C_PATCHES.md

main.c Patches for Phan-in-Browser

This document describes the patches applied to PHP's main/main.c file for each PHP version.

Purpose

The phan-demo uses PHP's embed SAPI to run PHP code in WebAssembly. By default, PHP's embed SAPI doesn't write errors to stderr when display_errors = "stderr" is set. The patch removes the SAPI name check to allow stderr output regardless of SAPI.

Patch Details

Single Modification

The patch modifies the error display logic in the php_error_cb function:

Original code:

/* Write CLI/CGI errors to stderr if display_errors = "stderr" */
if ((!strcmp(sapi_module.name, "cli") || !strcmp(sapi_module.name, "cgi") || !strcmp(sapi_module.name, "phpdbg")) &&
    PG(display_errors) == PHP_DISPLAY_ERRORS_STDERR
) {
    fprintf(stderr, "%s: ", error_type_str);
    // ... error output ...
}

Patched code:

/* Write errors to stderr if display_errors = "stderr" regardless of sapi (Phan Demo patch for "embed" sapi) */
if (
    PG(display_errors) == PHP_DISPLAY_ERRORS_STDERR
) {
    fprintf(stderr, "%s: ", error_type_str);
    // ... error output ...
}

Changes Made

1. Removed SAPI name checks: !strcmp(sapi_module.name, "cli"), etc.
2. Updated comment to reflect the change
3. This allows the "embed" SAPI (used by WebAssembly) to write errors to stderr

Version-Specific Files

PHP 8.1 (main-8.1.c)

• Source: PHP 8.1 branch from php-src
• Patch line: ~1345
• Additional notes: PHP 8.1 had some ini handler simplifications already applied

PHP 8.2 (main-8.2.c)

• Source: PHP 8.2 branch from php-src
• Patch line: ~1359
• Additional notes: Similar structure to 8.1

PHP 8.3 (main-8.3.c)

• Source: PHP 8.3 branch from php-src
• Patch line: ~1370
• Additional notes: Uses fwrite() for message output (slightly different from other versions)

PHP 8.4 (main-8.4.c)

• Source: PHP 8.4 branch from php-src
• Patch line: ~1411
• Additional notes: This was the original version used

PHP 8.5 (main-8.5.c)

• Source: PHP 8.5 branch from php-src
• Patch line: ~1482
• Additional notes: Latest development version

Why Version-Specific Files?

PHP's internal API changes between versions. While the patch is conceptually the same, the exact line numbers and surrounding code differ. Using version-specific files ensures:

1. Compatibility: Each PHP version gets the correct patch
2. Maintainability: Easy to update patches when PHP versions change
3. Reliability: No risk of applying patches to wrong line numbers

Generating Patches

If you need to update or regenerate these patches:

1. Checkout the desired PHP version branch in php-src:

   cd ~/php-src
   git checkout PHP-8.X

2. Copy the original main.c:

   cp main/main.c /path/to/phan-demo/main-8.X.c

3. Apply the patch:

   cd /path/to/phan-demo
   # Update comment
   sed -i 's|Write CLI/CGI errors to stderr|Write errors to stderr if display_errors = "stderr" regardless of sapi (Phan Demo patch for "embed" sapi)|' main-8.X.c
   
   # Remove SAPI check
   line=$(grep -n 'if ((!strcmp(sapi_module.name, "cli")' main-8.X.c | cut -d: -f1)
   sed -i "${line}s|.*if ((!strcmp.*|\t\t\t\t\tif (|" main-8.X.c

4. Verify the patch:

   # Check the patched section
   sed -n "$((line-1)),$((line+6))p" main-8.X.c

Testing

After applying patches, verify by:

1. Building the specific PHP version
2. Running sample code with intentional errors
3. Confirming errors appear in stderr output
4. Testing with display_errors = "stderr" in pib_eval.c

Future Considerations

PHP 8.6+

When new PHP versions are released:

1. Create new main-8.X.c file using the process above
2. Add version to PHP_VERSIONS array in build-multi.sh
3. Update index.html dropdown with new version
4. Update documentation

Alternative Approaches

Instead of patching main.c, alternatives could include:

• Setting display_errors = 1 and capturing output differently
• Modifying pib_eval.c to redirect output streams
• Using a custom error handler in PHP code

However, the main.c patch is the cleanest solution as it allows proper stderr output at the PHP level.