Re: [Buildroot] [PATCH v3 1/1] package/libxml2: fix compilation with uclibc

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello Dario,

On Fri, 27 Dec 2024 18:42:46 +0100
Dario Binacchi <dario.binacchi@amarulasolutions.com> wrote:

> The patch fixes the following errors and warnings raised by the
> compilation of the library with uClibc:
> 
> encoding.c: In function ‘xmlEncInputChunk’:
> encoding.c:2209:32: warning: comparison between pointer and integer
>  2209 |     else if (handler->iconv_in != NULL) {
>       |                                ^~
> encoding.c: In function ‘xmlEncOutputChunk’:
> encoding.c:2269:33: warning: comparison between pointer and integer
>  2269 |     else if (handler->iconv_out != NULL) {
>       |                                 ^~
> encoding.c: In function ‘xmlCharEncCloseFunc’:
> encoding.c:2681:29: warning: comparison between pointer and integer
>  2681 |     if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
>       |                             ^~
> encoding.c:2681:60: warning: comparison between pointer and integer
>  2681 |     if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
>       |                                                            ^~
> encoding.c:2683:32: warning: comparison between pointer and integer
>  2683 |         if (handler->iconv_out != NULL) {
>       |                                ^~
> encoding.c:2686:32: error: assignment to ‘iconv_t’ {aka ‘long int’} from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
>  2686 |             handler->iconv_out = NULL;
>       |                                ^
> encoding.c:2688:31: warning: comparison between pointer and integer
>  2688 |         if (handler->iconv_in != NULL) {
>       |                               ^~
> encoding.c:2691:31: error: assignment to ‘iconv_t’ {aka ‘long int’} from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
>  2691 |             handler->iconv_in = NULL;
>       |                               ^
> make[4]: *** [Makefile:1147: libxml2_la-encoding.lo] Error 1
> 
> The regression was partially introduced in version 2.1.0:
> 496a1cf59284 ("496a1cf59284 revamped the encoding support, added iconv support, so now libxml if")
> and partially in version 2.2.3:
> 87b953957305 ("Large sync between my W3C base and Gnome's one:")
> 
> So the regression was already present in the first version of libxml2
> (2.6.29) in Buildroot.
> 
> Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> ---

Thanks for the patch and investigation. However the explanation was not
really complete: it is clearly impossible that this build failure
existed with uClibc since libxml2 was introduced in Buildroot. Indeed,
uClibc used to be the only C library in Buildroot, it has been the
default for many years, etc.

So in fact, the issue started occurring only since GCC 14.x was
introduced. It used to be a warning, and GCC 14.x turned it into a hard
build error. Also, it appears only with uClibc because uClibc defines
iconv_t as "long", while both glibc and musl define it as "void *".

I have updated the commit log with those details, I've added a
reference to the autobuilder failure being fixed in the commit log, and
updated the Upstream: link in the patch to point to the upstream commit.

Thanks for this great investigation work!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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