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Date: Fri, 20 Aug 2021 18:02:36 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Andrii Nakryiko <andriin@...com>, dwarves@...r.kernel.org,
netdev@...r.kernel.org, bpf@...r.kernel.org,
Alexei Starovoitov <ast@...nel.org>,
Yonghong Song <yhs@...com>, Hao Luo <haoluo@...gle.com>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>,
Nathan Chancellor <nathan@...nel.org>,
Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [RFC] dwarves/pahole: Add test scripts
Em Fri, Aug 20, 2021 at 05:39:22PM -0300, Arnaldo Carvalho de Melo escreveu:
> So, now looking at:
> test_btfdiff on /var/home/acme/.pahole_test_objects/x86-gcc/vmlinux ... FAIL
Minor stuff, why would BTF get that const and DWARF not?
⬢[acme@...lbox pahole]$ btfdiff /var/home/acme/.pahole_test_objects/x86-gcc/vmlinux
--- /tmp/btfdiff.dwarf.j8SZhr 2021-08-20 17:40:52.052186096 -0300
+++ /tmp/btfdiff.btf.5QMi8C 2021-08-20 17:40:52.298191569 -0300
@@ -33719,7 +33719,7 @@ struct e1000_option {
/* XXX 4 bytes hole, try to pack */
- struct e1000_opt_list * p; /* 40 8 */
+ const struct e1000_opt_list * p; /* 40 8 */
} l; /* 32 16 */
} arg; /* 32 16 */
⬢[acme@...lbox pahole]$ btfdiff /var/home/acme/.pahole_test_objects/x86-clang/vmlinux
--- /tmp/btfdiff.dwarf.1TAWtj 2021-08-20 17:41:18.821781610 -0300
+++ /tmp/btfdiff.btf.FMLZRt 2021-08-20 17:41:19.058786883 -0300
@@ -21584,7 +21584,7 @@ struct cpu_rmap {
struct {
u16 index; /* 16 2 */
u16 dist; /* 18 2 */
- } near[0]; /* 16 0 */
+ } near[]; /* 16 0 */
/* size: 16, cachelines: 1, members: 5 */
/* last cacheline: 16 bytes */
@@ -65743,7 +65743,7 @@ struct linux_efi_memreserve {
struct {
phys_addr_t base; /* 16 8 */
phys_addr_t size; /* 24 8 */
- } entry[0]; /* 16 0 */
+ } entry[]; /* 16 0 */
/* size: 16, cachelines: 1, members: 4 */
/* last cacheline: 16 bytes */
@@ -72814,7 +72814,7 @@ struct netlink_policy_dump_state {
struct {
const struct nla_policy * policy; /* 16 8 */
unsigned int maxtype; /* 24 4 */
- } policies[0]; /* 16 0 */
+ } policies[]; /* 16 0 */
/* size: 16, cachelines: 1, members: 4 */
/* sum members: 12, holes: 1, sum holes: 4 */
⬢[acme@...lbox pahole]$o
I see, there are two declarations for this struct, one at:
drivers/net/ethernet/intel/e1000/e1000_param.c
166 struct e1000_option {
167 enum { enable_option, range_option, list_option } type;
168 const char *name;
169 const char *err;
170 int def;
171 union {
172 struct { /* range_option info */
173 int min;
174 int max;
175 } r;
176 struct { /* list_option info */
177 int nr;
178 const struct e1000_opt_list { int i; char *str; } *p;
179 } l;
180 } arg;
181 };
and the other at (note that extra 'e' after 1000 :) ):
drivers/net/ethernet/intel/e1000e/param.c
141 struct e1000_option {
142 enum { enable_option, range_option, list_option } type;
143 const char *name;
144 const char *err;
145 int def;
146 union {
147 /* range_option info */
148 struct {
149 int min;
150 int max;
151 } r;
152 /* list_option info */
153 struct {
154 int nr;
155 struct e1000_opt_list {
156 int i;
157 char *str;
158 } *p;
159 } l;
160 } arg;
161 };
The only difference is that 'const'.
I _guess_ that the BTF deduplicator is picking the one with the 'const'
while pahole's (which is just used when pretty printing, not when BTF
encoding) with the other (it shouldn't as per my intention, I'm not
arguing about if both should appear as different types).
I tested it with:
pahole -j -F dwarf -C e1000_option /var/home/acme/.pahole_test_objects/x86-gcc/vmlinux
to use the new DWARF multithreaded loading, like 'btfdiff' now does, and
its related to which of these types get loaded first, but its just
related to pahole pretty printing, not for the BTF encoding, where all
types will be passed to BTF for deduplication.
Same thing happens with clang, its just that when pretty printing in
this test run the clang multithreaded DWARF loading saw the type that
BTF picked (the one with 'const').
When I re-run it with:
⬢[acme@...lbox pahole]$ git diff
diff --git a/btfdiff b/btfdiff
index 77543630d1965b5e..71d3dbf5fc861e16 100755
--- a/btfdiff
+++ b/btfdiff
@@ -26,7 +26,6 @@ pahole_bin=${PAHOLE-"pahole"}
${pahole_bin} -F dwarf \
--flat_arrays \
--sort \
- --jobs \
--suppress_aligned_attribute \
--suppress_force_paddings \
--suppress_packed \
⬢[acme@...lbox pahole]$ git diff
I get:
test_btfdiff on /var/home/acme/.pahole_test_objects/aarch64-clang/vmlinux ... OK
test_btfdiff on /var/home/acme/.pahole_test_objects/x86-clang/vmlinux ... FAIL
clang's is just that zero entries array diff again.
I'll get 1.22 out of the door tomorrow as it passed these tests and also
the ones at libbpf github CI and my local ones and get these scripts merged
in 1.23, will check the clang output as well.
Thanks for the scripts!
- Arnaldo
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