Seems like ppc32 kernel pass the application entry point address
in r7 and MSR in r8 when starting the application. The source might be
ret_from_syscall, in entry.S:
...
lwz r7,_NIP(r1)
lwz r8,_MSR(r1)
FIX_SRR1(r8, r0)
lwz r2,GPR2(r1)
lwz r1,GPR1(r1)
mtspr SPRN_SRR0,r7
mtspr SPRN_SRR1,r8
SYNC
RFI
I am not convinced this is the source, but a non zero r7
breaks static apps in uClibc.
Is this on purpose and why?
Secion 8.4.1 in
http://refspecs.freestandards.org/LSB_3.1.0/LSB-Core-PPC32/LSB-Core-PPC32.html#PROCESSINITIALIZATION
says:
"Contrary to what is stated in the Registers part of chapter 3 of the System V Application Binary Interface PowerPC Processor
Supplement there are no values set in registers r3, r4, r5, r6 and r7. Instead the values specified to appear in all of those
registers except r7 are placed on the stack. The value to be placed into register r7, the termination function pointer is not passed
to the process."
How do one not pass a termination function in r7 other than setting
r7 to zero?
Jocke
On Fri, 2005-12-09 at 00:07 +0100, Tjernlund wrote:
Seems like ppc32 kernel pass the application entry point address
in r7 and MSR in r8 when starting the application. The source might be
ret_from_syscall, in entry.S:
...
lwz r7,_NIP(r1)
lwz r8,_MSR(r1)
FIX_SRR1(r8, r0)
lwz r2,GPR2(r1)
lwz r1,GPR1(r1)
mtspr SPRN_SRR0,r7
mtspr SPRN_SRR1,r8
SYNC
RFI
I am not convinced this is the source, but a non zero r7
breaks static apps in uClibc.
Is this on purpose and why?
Secion 8.4.1 in
http://refspecs.freestandards.org/LSB_3.1.0/LSB-Core-PPC32/LSB-Core-PPC32.html#PROCESSINITIALIZATION
says:
"Contrary to what is stated in the Registers part of chapter 3 of the System V Application Binary Interface PowerPC Processor
Supplement there are no values set in registers r3, r4, r5, r6 and r7. Instead the values specified to appear in all of those
registers except r7 are placed on the stack. The value to be placed into register r7, the termination function pointer is not passed
to the process."
How do one not pass a termination function in r7 other than setting
r7 to zero?
Just ignore those registers on entry. The semantics of a syscall are to
clobber all volatile registers and there is no point doing anything
else.
Ben.
Tjernlund writes:
Secion 8.4.1 in
http://refspecs.freestandards.org/LSB_3.1.0/LSB-Core-PPC32/LSB-Core-PPC32.html#PROCESSINITIALIZATION
says:
"Contrary to what is stated in the Registers part of chapter 3 of the System V Application Binary Interface PowerPC Processor
Supplement there are no values set in registers r3, r4, r5, r6 and r7. Instead the values specified to appear in all of those
registers except r7 are placed on the stack. The value to be placed into register r7, the termination function pointer is not passed
to the process."
How do one not pass a termination function in r7 other than setting
r7 to zero?
"Not passed" means that there is no value provided in any register or
word of memory that should be taken to be the address of a termination
function.
Paul.