Add template support for "--enable-debug" flag

[yosifkit]

DOCKER_PHP_ENABLE_DEBUG is not used or supported by official-images; this is for users who want to build their own php image with debug enabled

This will allow power users to generate their own PHP Dockerfiles with debug enabled. This is explicitly written to not change the regular versions of the Dockerfiles (i.e. running ./apply-templates.sh will result in no change). I have build tested one or two versions and they seem to work:

$ docker build 8.0/alpine3.16/cli/
...
Successfully built 7feb88eade75
$ docker run -it --rm 7feb88eade75 php -i
...
Debug Build => yes
...

To regenerate all the Dockerfiles with debug enabled (bash, jq, gawk, and wget are required to run it):

$ DOCKER_PHP_ENABLE_DEBUG=1 ./apply-templates
processing 8.0/bullseye/cli ...
processing 8.0/bullseye/apache ...
[...]
processing 8.2-rc/alpine3.16/fpm ...
processing 8.2-rc/alpine3.16/zts ...

Alternative to #1287 and #1280.

Closes #1287
Closes #1280

[enumag]

I believe that #1280 is still relevant even with this, right?

[tianon]

Nope, the generated Dockerfiles from this will not include the strip block at all.

[tianon]

An example full generated diff, to illustrate:

diff --git a/8.1/bullseye/cli/Dockerfile b/8.1/bullseye/cli/Dockerfile
index 3609c4f2..954ceae5 100644
--- a/8.1/bullseye/cli/Dockerfile
+++ b/8.1/bullseye/cli/Dockerfile
@@ -174,18 +174,11 @@ RUN set -eux; \
 		\
 # https://github.com/docker-library/php/pull/939#issuecomment-730501748
 		--enable-embed \
+		--enable-debug \
 	; \
 	make -j "$(nproc)"; \
 	find -type f -name '*.a' -delete; \
 	make install; \
-	find \
-		/usr/local \
-		-type f \
-		-perm '/0111' \
-		-exec sh -euxc ' \
-			strip --strip-all "$@" || : \
-		' -- '{}' + \
-	; \
 	make clean; \
 	\
 # https://github.com/docker-library/php/issues/692 (copy default example "php.ini" files somewhere easily discoverable)

[enumag]

@yosifkit @tianon Can we get this merged? I'd like to use it.

[joehoyle]

This looks great. We'd like to be able to build a variant of the image without stripping symbols. This is especially useful when trying to debug core dumps. With the stripped binary it's very difficult to debug a core dump meaningfully. However, it seems in this PR this is tied to the --enable-debug build of PHP. As far as I understand, one can not take a core dump generated by a non-debug build (which you'd use in production) and later use gdb with the php build that has been built with --enable-debug.

If that's the use-case this PR is trying to address, I wanted to highlight it as a concern.

[enumag]

Yeah... I wasn't aware that --enable-debug isn't required to get backtrace from core dumps until yesterday. Indeed it would be better if there was a separate flag to disable symbol stripping while keeping debug disabled.

[joehoyle]

On that topic, for better backtraces adding -g2 to the CFLAGS will remove some optimizations, which will gives more frames etc in the backtrace. In my testing, it's safe to use -g2 on a "debug" (not --enable-debug) build of PHP for reading production code dumps.

[tianon]

I'm going to merge this -- I'm still really concerned about it, because we will not be testing it, especially over time, and we cannot guarantee it will continue to work properly in the future, but I hope the comments in the template make that clear enough.

[WoZ]

It is worth mentioning, that the image built with DOCKER_PHP_ENABLE_DEBUG will not have sources required for listing of the code.

Reading symbols from php-fpm...
(gdb) start
Temporary breakpoint 1 at 0x897d14: file /usr/src/php/sapi/fpm/fpm/fpm_main.c, line 1532.
Starting program: /usr/local/sbin/php-fpm -F
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/aarch64-linux-gnu/libthread_db.so.1".

Temporary breakpoint 1, main (argc=2, argv=0xfffffffffa38) at /usr/src/php/sapi/fpm/fpm/fpm_main.c:1532
1532	/usr/src/php/sapi/fpm/fpm/fpm_main.c: No such file or directory.

To fix this run

docker-php-source extract

Inside the container (or make it the part of the building process).

After extraction

Reading symbols from php-fpm...
(gdb) start
Temporary breakpoint 1 at 0x897d14: file /usr/src/php/sapi/fpm/fpm/fpm_main.c, line 1532.
Starting program: /usr/local/sbin/php-fpm -F
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/aarch64-linux-gnu/libthread_db.so.1".

Temporary breakpoint 1, main (argc=2, argv=0xfffffffffa38) at /usr/src/php/sapi/fpm/fpm/fpm_main.c:1532
1532	{
(gdb) list
1527		STANDARD_MODULE_PROPERTIES
1528	};
1529
1530	/* {{{ main */
1531	int main(int argc, char *argv[])
1532	{
1533		int exit_status = FPM_EXIT_OK;
1534		int cgi = 0, c, use_extended_info = 0;
1535		zend_file_handle file_handle;
1536
(gdb)