riscv: Fix crash when syscall argument reg index is too high

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Submitter:	Alec Roelke
Repository:	gem5
Branch:	default
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Description

Changeset 11795:3ac8305dbf60
---------------------------
riscv: Fix crash when syscall argument reg index is too high

By default, doSyscall gets the values of six registers to be used for
system call arguments.  RISC-V, by convention, only has four.  Because
RISC-V's implementation of these indices is as arrays of integers rather
than as base indices plus offsets, trying to get the fifth argument
register's value will cause a crash.  This patch fixes that by returning 0
for any index higher than 3.

Testing Done

Issue Summary

Description	From	Last Updated	Status
Two comments: 1. Shouldn't this at least have a warning? If the syscall arg register > 3 there is definitely ...	Jason Lowe-Power	Jan. 18, 2017, 9:40 a.m.	Resolved

src/arch/riscv/process.cc (Diff revision 1)

Two comments:

1. Shouldn't this at least have a warning? If the syscall arg register > 3 there is definitely a bug, right?

2. Can you return "0" instead of the last register? I think that's a better failover case.

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Alec Roelke Jan. 18, 2017, 8:38 a.m. (Jan. 18, 2017, 8:38 a.m.)

Returning 0 would make more sense, so I'll do that.  I can also add a warning, but that causes a minimum of two warnings to print every system call since the doSyscall() function gathers the values of the system call registers from indices 0 to 5 every time a system call is made.  This is only used for a debug statement, though; is there a reason it does this even when debugging is off?

Jason Lowe-Power Jan. 18, 2017, 9:02 a.m. (Jan. 18, 2017, 9:02 a.m.)

Ah. In this case, don't worry about adding a "warn". We'll just have to assume that anyone who implements a syscall in RISC-V will know not to use the values in registers > 3.
It would be good to add a comment when you update to return 0.

Description:

~		Changeset 11795:44b4eec15cd7
	~	Changeset 11795:3ac8305dbf60

		riscv: Fix crash when syscall argument reg index is too high

		By default, doSyscall gets the values of six registers to be used for
		system call arguments. RISC-V, by convention, only has four. Because
		RISC-V's implementation of these indices is as arrays of integers rather
		than as base indices plus offsets, trying to get the fifth argument
~		register's value will cause a crash. This patch fixes that by providing
~		the fourth register's value for any index higher than 3.
	~	register's value will cause a crash. This patch fixes that by returning 0
	~	for any index higher than 3.

Diff:

Revision 2 (+7 -1)

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src/arch/riscv/process.cc

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Description:

Changeset 11795:44b4eec15cd7

Changeset 11795:3ac8305dbf60

Diff:

Status: Closed (submitted)