Syscalls: Make system calls access arguments like a stack, not an array.

When accessing arguments for a syscall, the position of an argument depends on
the policies of the ISA, how much space preceding arguments took up, and the
"alignment" of the index for this particular argument into the number of
possible storate locations. This change adjusts getSyscallArg to take its
index parameter by reference instead of value and to adjust it to point to the
possible location of the next argument on the stack, basically just after the
current one. This way, the rules for the new argument can be applied locally
without knowing about other arguments since those have already been taken into
account implicitly.

All system calls have also been changed to reflect the new interface. In a
number of cases this made the implementation clearer since it encourages
arguments to be collected in one place in order and then used as necessary
later, as opposed to scattering them throughout the function or using them in
place in long expressions. It also discourages using getSyscallArg over and
over to retrieve the same value when a temporary would do the job.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/arch/arm/linux/process.cc b/src/arch/arm/linux/process.cc
index a7f36e18d..f909d871a 100644
--- a/src/arch/arm/linux/process.cc
+++ b/src/arch/arm/linux/process.cc
@@ -50,7 +50,8 @@ static SyscallReturn
 unameFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
           ThreadContext *tc)
 {
-    TypedBufferArg<Linux::utsname> name(process->getSyscallArg(tc, 0));
+    int index = 0;
+    TypedBufferArg<Linux::utsname> name(process->getSyscallArg(tc, index));
 
     strcpy(name->sysname, "Linux");
     strcpy(name->nodename, "m5.eecs.umich.edu");
@@ -417,7 +418,8 @@ static SyscallReturn
 setTLSFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
           ThreadContext *tc)
 {
-    uint32_t tlsPtr = process->getSyscallArg(tc, 0);
+    int index = 0;
+    uint32_t tlsPtr = process->getSyscallArg(tc, index);
 
     tc->getMemPort()->writeBlob(ArmLinuxProcess::commPage + 0x0ff0,
                                 (uint8_t *)&tlsPtr, sizeof(tlsPtr));
@@ -511,12 +513,12 @@ ArmLinuxProcess::startup()
 }
 
 ArmISA::IntReg
-ArmLinuxProcess::getSyscallArg(ThreadContext *tc, int i)
+ArmLinuxProcess::getSyscallArg(ThreadContext *tc, int &i)
 {
     // Linux apparently allows more parameter than the ABI says it should.
     // This limit may need to be increased even further.
     assert(i < 6);
-    return tc->readIntReg(ArgumentReg0 + i);
+    return tc->readIntReg(ArgumentReg0 + i++);
 }
 
 void