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SubjectRe: proxy_pda was Re: What was in the x86 merge for .20
Date
Hi,

I've reviewed the thread and can propose a solution.
Let's see e.g. the dev.s ( from fuse.ko ). Currently with gcc-4.2 we get:

fuse_req_init_context:
movl $_proxy_pda+8, %edx #, tmp62
#APP
movl %gs:8,%ecx #, ret__
#NO_APP
movl 344(%ecx), %ecx # <variable>.fsuid, <variable>.fsuid
movl %ecx, 60(%eax) # <variable>.fsuid, <variable>.in.h.uid
#APP
movl %gs:8,%ecx #, ret__
#NO_APP
movl 360(%ecx), %ecx # <variable>.fsgid, <variable>.fsgid
movl %ecx, 64(%eax) # <variable>.fsgid, <variable>.in.h.gid
#APP
movl %gs:8,%edx #, ret__
#NO_APP
movl 164(%edx), %edx # <variable>.pid, <variable>.pid
movl %edx, 68(%eax) # <variable>.pid, <variable>.in.h.pid
ret

In this scenario gcc is explictly blocked by -fno-strict-aliasing
and massive %gs:8 reloads are present. If you fix aliasing violations
in kernel then you could use -fstrict-aliasing to get what you want.

fuse_req_init_context:
#APP
movl %gs:8,%ecx #, ret__
#NO_APP
movl 344(%ecx), %edx # <variable>.fsuid, <variable>.fsuid
movl %edx, 60(%eax) # <variable>.fsuid, <variable>.in.h.uid
movl 360(%ecx), %edx # <variable>.fsgid, <variable>.fsgid
movl %edx, 64(%eax) # <variable>.fsgid, <variable>.in.h.gid
movl 164(%ecx), %edx # <variable>.pid, <variable>.pid
movl %edx, 68(%eax) # <variable>.pid, <variable>.in.h.pid
ret

BR,
Pawel.
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