INCBIN changes .section for subsequent code

[Habbie]

(full background, with some overhead, at https://github.com/PowerDNS/pdns/issues/9835#issuecomment-741748081)

We have this piece of code:

INCBIN(api_swagger_yaml, "api-swagger.yaml");
static const string g_api_swagger_yaml{(const char*)gapi_swagger_yamlData, gapi_swagger_yamlSize};
INCBIN(api_swagger_json, "api-swagger.json");
static const string g_api_swagger_json{(const char*)gapi_swagger_jsonData, gapi_swagger_jsonSize};

When we compile this with gcc's or clang's Address Sanitizer, it crashes in a string constructor.

Reordering the code like this fixes the problem:

INCBIN(api_swagger_yaml, "api-swagger.yaml");
INCBIN(api_swagger_json, "api-swagger.json");
static const string g_api_swagger_yaml{(const char*)gapi_swagger_yamlData, gapi_swagger_yamlSize};
static const string g_api_swagger_json{(const char*)gapi_swagger_jsonData, gapi_swagger_jsonSize};

A copy/paste of my understanding of the reason, from the linked ticket:

• INCBIN sets .section rodata
• the compiler sets .bss for storing the const string
• the next INCBIN call sets .section rodata again
• the compiler omits .bss for the second const string - presumably because it assumes it is already in BSS

Now the question is - can we add something to the macro to 'restore' the previously active section, or inform the compiler that it needs to repeat its section choice?

[graphitemaster]

I think it may be possible to reset to the .text.

[Theldus]

Maybe .pushsection and .popsection?, I haven't used these before, so maybe I'm equivocated.

[hhoffstaette]

Hi! I encountered this problem when building a C++ program which refused to link with LTO, and found the solution in the GCC bug tracker: 78613 and 47071. The fix was indeed simple:

diff -up incbin.h~ incbin.h
--- incbin.h~   2018-11-12 09:33:58.000000000 +0100
+++ incbin.h    2021-03-13 17:53:28.552595628 +0100
@@ -216,6 +216,7 @@
             INCBIN_MANGLE INCBIN_STRINGIZE(INCBIN_PREFIX) #NAME "Size:\n" \
                 INCBIN_INT INCBIN_MANGLE INCBIN_STRINGIZE(INCBIN_PREFIX) #NAME "End - " \
                            INCBIN_MANGLE INCBIN_STRINGIZE(INCBIN_PREFIX) #NAME "Data\n" \
+            ".previous" "\n" \
     ); \
     INCBIN_EXTERN(NAME)

..and voilà: no more section mismatches during linking :smile:

[graphitemaster]

This is a good solution to the problem. I just need to make sure .previous works on all the assembler toolchains.

[graphitemaster]

It looks like this is already fixed with resetting back to the .text section so I sense you just have an out of date copy of incbin maybe?

[hhoffstaette]

It looks like this is already fixed with resetting back to the .text section so I sense you just have an out of date copy of incbin maybe?

I used (and patched) the one that came bundled with the source of the package that had problems, and that didn't yet have the fix on master. However said package no loger uses incbin, so .. ¯\_(ツ)_/¯