On 7/5/22 10:00 PM, Andrii Nakryiko wrote:
On Sun, Jul 3, 2022 at 10:53 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
On Sun, Jul 03, 2022 at 09:09:24PM +0800, Yixun Lan wrote:
Enable this option to fix a bcc error in RISC-V platform
And, the error shows as follows:
These should not be enabled on new platforms. Use the proper helpers
to probe kernel vs user pointers instead.
riscv existed as of [0], so I'd argue it is a proper bug fix, as
corresponding select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE should
have been added back then.
But I also agree that BCC tools should be updated to use proper
bpf_probe_read_{kernel,user}[_str()] helpers, please contribute such
fixes to BCC tools and BCC itself as well. Cc'ed Alan as his ksnoop in
libbpf-tools seems to be using bpf_probe_read() as well and needs to
be fixed.
Yixun, the bcc change looks like below:
--- a/src/cc/frontends/clang/b_frontend_action.cc
+++ b/src/cc/frontends/clang/b_frontend_action.cc
@@ -132,7 +132,7 @@ static std::string
check_bpf_probe_read_user(llvm::StringRef probe,
/* For arch with overlapping address space, dont use
bpf_probe_read for
* user read. Just error out */
-#if defined(__s390x__)
+#if defined(__s390x__) || defined(__riscv_)
overlap_addr = true;
return "";
#endif
Basically, prevent using bpf_probe_read() helper, so it will force user
to use bpf_probe_read_user() or bpf_probe_read_kernel(). and this should
make it work for old kernels.
[0] 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}() only to
archs where they work")
