[PATCH v3 09/29] loongarch: Add <bits/pagesize.h>

[Florian Weimer]

* Xi Ruoyao:

> On Sun, 2024-09-29 at 18:12 +0200, Florian Weimer wrote:
>> According to arch/loongarch/Kconfig in the kernel sources, LoongArch
>> supports 4 KiB, 16 KiB, and 64 KiB page sizes.
>
> As reported
> at https://github.com/loongson-community/discussions/issues/47, 64KiB
> configuration currently does not work at all because ld sets an
> insufficient alignment in the program header:
>
>   LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
>                  0x0000000000000850 0x0000000000000850  R E    0x4000
>   LOAD           0x0000000000003df8 0x0000000000007df8 0x0000000000007df8
>                  0x0000000000000230 0x0000000000000238  RW     0x4000
>
> So to me we should either raise the alignment to 0x10000, or remove the
> 64 KiB page support to simplify the code everywhere.

I think it's more important that the lower 16 bits of the file offset
and the virtual address are the same.  The alignment should actuallt be
4 KiB, otherwise the glibc loader will do extra work on 4 KiB machines
because it cannot know if the alignment really has to be 16 KiB
(or 64 KiB), or if it's just a toolchain default.

> How do you think?

On the glibc side, there is only a simplification if there's just one
page size to support.  It doesn't make a difference if there are two,
three, or more.

>> Note: The entire series runs into a GCC compilation problem on
>> LoongArch, which appears to be a GCC bug:
>> 
>>   Section type conflict on loongarch with .data.rel.ro section attribute
>>   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116887
>
> I'm taking a look.  But still we should try to work around it on the
> Glibc side.  Otherwise even if we fix it for GCC we'd still need to
> raise the required GCC version to the leading edge, and doing so is bad
> for users and distro maintainers.

We can do this:

diff --git a/sysdeps/unix/sysv/linux/loongarch/dl-find_object.c b/sysdeps/unix/sysv/linux/loongarch/dl-find_object.c
new file mode 100644
index 0000000000..63f055bd40
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/loongarch/dl-find_object.c
@@ -0,0 +1,4 @@
+/* Work around GCC PR116887.  */
+#undef attribute_relro
+#define attribute_relro
+#include <elf/dl-find_object.c>

But maybe there is a better option.

Thanks,
Florian