Re: [PATCH][wwwdocs] gcc-13: Add loongarch '-mexplicit-relocs' support

[Lulu Cheng <chenglulu@loongson.cn>]

在 2022/7/26 下午8:01, Xi Ruoyao 写道:
> On Tue, 2022-07-26 at 19:42 +0800, Lulu Cheng wrote:
>
>> 在 2022/7/26 下午5:44, Xi Ruoyao 写道:
>>> Should we indicate that our .eh_frame section format has changed?
> I don't really understand C++ exception handling, so: does the change
> breaks something?  For example, if foo links to libbar, libbar is built
> with GCC 12 (or vice versa), would an exception thrown from libbar
> properly caught by foo?
>
> Generally changes.html is for compiler users (instead of developers),
> and I believe at least 90% of users (including I) don't know the
> potential consequences from a .eh_frame format change.  So it's better
> to describe the breakage and possible workaround here.  If nothing will
> be broken, we can just skip the change in changes.html.
>
>
The ASM_PREFERRED_EH_DATA_FORMAT macro before and after modification is 
as follows:

  #define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL) \

-  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_absptr)
+  (((GLOBAL) ? DW_EH_PE_indirect : 0) | DW_EH_PE_pcrel | DW_EH_PE_sdata4)

Use the following tests to describe the effect of modifying this macro 
on the generated assembly code： #include <iostream> #include <exception> 
using namespace std; int main() { 　　try { 　　throw 1; 　　} 　　catch 
(int i) 　　{ 　　　　cout << i << endl; 　　} } The main comparisons 
related to the eh_frame section are as follows： 　　　　　　 OLD NEW 
.LFB1997 = . | .LFB1780 = . .cfi_startproc | .cfi_startproc 
.cfi_personality 0x80,DW.ref.__gxx_personality_v0 | .cfi_personality 
0x9b,DW.ref.__gxx_personality_v0 .cfi_lsda 0,.LLSDA1997 | .cfi_lsda 
0x1b,.LLSDA1780 If the assembly file generated by the new gcc is 
compiled with the binutils of version 2.38, the following error will be 
reported: test.s:74: Error: invalid or unsupported encoding in 
.cfi_personality test.s:75: Error: invalid or unsupported encoding in 
.cfi_lsda

So I think I should judge whether binutils supports this encoding when 
gcc is configured, and then choose how to define macro 
ASM_PREFERRED_EH_DATA_FORMAT.