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Wed, 24 Jul 2024 09:28:29 +0000 Message-ID: <0f4d0d87-458f-482d-af49-fc6a65b15daa@suse.de> Date: Wed, 24 Jul 2024 11:28:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] [gdb/testsuite] Add xfail in gdb.base/hbreak.exp To: Luis Machado , gdb-patches@sourceware.org References: <20240717151055.21480-1-tdevries@suse.de> <6ad9fbd8-1977-4688-9534-00d1271bba99@arm.com> <6d4a4345-0247-4c1f-9db3-e0347b475e4b@suse.de> <4e82e0bc-3e3a-4461-be2d-7b8d4785e1a5@arm.com> Content-Language: en-US From: Tom de Vries In-Reply-To: <4e82e0bc-3e3a-4461-be2d-7b8d4785e1a5@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Action: no action X-Rspamd-Queue-Id: 088261F38E X-Spam-Score: -6.30 X-Spam-Level: X-Spamd-Result: default: False [-6.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; DWL_DNSWL_MED(-2.00)[suse.de:dkim]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; XM_UA_NO_VERSION(0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCPT_COUNT_TWO(0.00)[2]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim, imap1.dmz-prg2.suse.org:rdns, imap1.dmz-prg2.suse.org:helo] X-Spam-Status: No, score=-10.9 required=5.0 tests=BAYES_00, BODY_8BITS, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org On 7/24/24 08:53, Luis Machado wrote: > On 7/24/24 06:25, Tom de Vries wrote: >> On 7/23/24 12:02, Luis Machado wrote: >>> On 7/17/24 16:14, Luis Machado wrote: >>>> On 7/17/24 16:10, Tom de Vries wrote: >>>>> On an aarch64-linux system with 32-bit userland running in a chroot, and using >>>>> target board unix/mthumb I get: >>>>> ... >>>>> (gdb) hbreak hbreak.c:27^M >>>>> Hardware assisted breakpoint 2 at 0x4004e2: file hbreak.c, line 27.^M >>>> >>>> That is a bit odd, but it goes through the compat layer, which is not exercised >>>> as often as the 32-bit code. >>>> >>>> Let me see if I can reproduce this one on my end. >>> >>> I managed to reproduce this. I checked with the kernel folks and this should >>> work, but I'm not sure where the error is coming from. >>> >> >> Hi Luis, >> >> thanks for looking into this, and the approval, committed. >> >> Are you or the kernel folks following up on this, in terms of a linux kernel PR or some such?  It would be nice to add some sort of reference to the xfail. > > It's in my TODO. I'm still investigating to understand where the error is coming from. Once located, I plan to check with them for their thoughts and a possible > fix. I don't think the kernel folks use the PR process much. We could probably ammend this commit later on once we have more information though. > Ok, I spent some more time debugging this issue this morning. After reading kernel sources for a while, I tried out reversing the order in which the Breakpoint Register Pair is written in arm_linux_nat_target::low_prepare_to_resume, and ... the test-case passes. My theory at this point is that the following happens in the failing case: - PTRACE_SETHBPREGS with address 0x4004e2 - compat_arch_ptrace - compat_ptrace_sethbpregs - compat_ptrace_hbp_set - ptrace_hbp_set_addr - ptrace_hbp_get_initialised_bp - ptrace_hbp_create - /* Initialise fields to sane defaults (i.e. values that will pass validation). */ attr.bp_len = HW_BREAKPOINT_LEN_4; - attr.bp_addr = 0x4004e2; - modify_user_hw_breakpoint - modify_user_hw_breakpoint_check - hw_breakpoint_parse - hw_breakpoint_arch_parse - case is_compat_bp(bp) - offset = 2; - fallthrough to default - return -EINVAL In short, we try to validate: - attr.bp_len == HW_BREAKPOINT_LEN_4 && attr.bp_addr == 0x4004e2 and fail. By reversing the order, we validate: - attr.bp_len == HW_BREAKPOINT_LEN_2 && attr.bp_addr == 0, and then - attr.bp_len == HW_BREAKPOINT_LEN_2 && attr.bp_addr == 0x4004e2 which both succeed. So, my questions at this point are: - is this a problem limited to aarch64 32-bit mode, or does it also occur for native 32-bit arm? - is this a kernel bug? - if this is a kernel bug, is there a workaround we can use? - if this is not a kernel bug, is this because gdb is writing the Breakpoint Register Pair in the wrong order? Thanks, - Tom >> >> Thanks, >> - Tom >> >>>> >>>> >>>>> (gdb) PASS: gdb.base/hbreak.exp: hbreak >>>>> continue^M >>>>> Continuing.^M >>>>> Unexpected error setting breakpoint: Invalid argument.^M >>>>> (gdb) FAIL: gdb.base/hbreak.exp: continue to break-at-exit after hbreak >>>>> ... >>>>> due to this call in arm_linux_nat_target::low_prepare_to_resume: >>>>> ... >>>>>            if (ptrace (PTRACE_SETHBPREGS, pid, >>>>>                (PTRACE_TYPE_ARG3) ((i << 1) + 1), &bpts[i].address) < 0) >>>>>              perror_with_name (_("Unexpected error setting breakpoint")); >>>>> ... >>>>> >>>>> This problem does not happen if instead we use a 4-byte aligned address. >>>>> >>>>> I'm not sure if this is simply unsupported or if there's a kernel bug of some >>>>> sort, but I don't see what gdb can do about this. >>>>> >>>>> Tentatively mark this as xfail. >>>>> >>>>> Tested on aarch64-linux. >>>>> --- >>>>>   gdb/testsuite/gdb.base/hbreak.exp | 40 ++++++++++++++++++++++++++----- >>>>>   1 file changed, 34 insertions(+), 6 deletions(-) >>>>> >>>>> diff --git a/gdb/testsuite/gdb.base/hbreak.exp b/gdb/testsuite/gdb.base/hbreak.exp >>>>> index 73a3e2afb67..b140257a23e 100644 >>>>> --- a/gdb/testsuite/gdb.base/hbreak.exp >>>>> +++ b/gdb/testsuite/gdb.base/hbreak.exp >>>>> @@ -27,10 +27,38 @@ if ![runto_main] { >>>>>     set breakline [gdb_get_line_number "break-at-exit"] >>>>>   -gdb_test "hbreak ${srcfile}:${breakline}" \ >>>>> -     "Hardware assisted breakpoint \[0-9\]+ at 0x\[0-9a-f\]+: file .*${srcfile}, line ${breakline}\\." \ >>>>> -     "hbreak" >>>>> +set re_loc "file \[^\r\n\]*$srcfile, line $breakline" >>>>> +set re_dot [string_to_regexp .] >>>>>   -gdb_test "continue" \ >>>>> -     "Continuing\\.\[ \r\n\]+Breakpoint \[0-9\]+, .*break-at-exit.*" \ >>>>> -     "continue to break-at-exit after hbreak" >>>>> +set addr 0x0 >>>>> +gdb_test_multiple "hbreak ${srcfile}:${breakline}" "hbreak" { >>>>> +    -re -wrap "Hardware assisted breakpoint $decimal at ($hex): $re_loc$re_dot" { >>>>> +    set addr $expect_out(1,string) >>>>> +    pass $gdb_test_name >>>>> +    } >>>>> +} >>>>> + >>>>> +set have_xfail 0 >>>>> +if { [istarget arm*-*-*] } { >>>>> +    # When running 32-bit userland on aarch64 kernel, thumb instructions that >>>>> +    # are not 4-byte aligned may not be supported for setting a hardware >>>>> +    # breakpoint on. >>>>> +    set have_xfail [expr ($addr & 0x2) == 2] >>>>> +} >>>>> + >>>>> +set re_xfail \ >>>>> +    [string_to_regexp \ >>>>> +     "Unexpected error setting breakpoint: Invalid argument."] >>>>> + >>>>> +gdb_test_multiple "continue" "continue to break-at-exit after hbreak" { >>>>> +    -re -wrap "Continuing\\.\[ \r\n\]+Breakpoint \[0-9\]+, .*break-at-exit.*" { >>>>> +    pass $gdb_test_name >>>>> +    } >>>>> +    -re -wrap $re_xfail { >>>>> +    if { $have_xfail } { >>>>> +        xfail $gdb_test_name >>>>> +    } else { >>>>> +        fail $gdb_test_name >>>>> +    } >>>>> +    } >>>>> +} >>>>> >>>>> base-commit: 0ed152c5c6b3c72fc505b331ed77e08b438d643a >>>> >>> >>> In any case, I agree gdb doesn't have a better way to deal with it. >>> >>> Approved-By: Luis Machado >> >