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westes / flex

The Fast Lexical Analyzer - scanner generator for lexing in C and C++
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flex should not always generate code that calls exit #133

Open taphqyu opened 7 years ago

taphqyu commented 7 years ago

Hey there, thanks for maintaining flex! I noticed that the default YY_FATAL_ERROR macro calls exit(). This doesn't feel right for something that's often going to be built into a low-level part of another program -- there should be a way to report the error out, and have the containing program decide what to do.

I don't see a way to provide an alternate YY_FATAL_ERROR definition right now because the macro is called in many different places with different semantics. For example, it's called from different helper functions that all return different data types, relying on the fact that YY_FATAL_ERROR never returns.

Would it be possible to refactor the fatal error reporting so that a user of flex can avoid calling exit()? For example, if I could provide a YY_FATAL_ERROR definition that let me store the error message in my yyextra, and then return 0 from yylex(), that would meet my need. Thanks!

whydoubt commented 7 years ago

As I had indicated, this is related to #194 . However, I believe this issue requires extra work to fix.

Explorer09 commented 7 years ago

Dammit. No! #133 and #194 are different!

133 is about calling exit in generated scanner code, while #194 is about exiting of flex generator itself.

westes commented 7 years ago

Oops, you're quite right. I got caught up in the paperwork and was moving too quickly yesterday.

saschmit commented 4 years ago

On the other hand, the lack of an enforced abort()/exit() caused Grub's YY_FATAL_ERROR handler to allow a buffer overflow: https://eclypsium.com/2020/07/29/theres-a-hole-in-the-boot/