+1 for using IR for hand-crafting tricky functions.
On 3 February 2016 at 22:01, Adrian Prantl via lldb-commits <lldb-commits@lists.llvm.org> wrote: > > On Feb 3, 2016, at 1:58 PM, Zachary Turner <ztur...@google.com> wrote: > > I was thinking of a really trivial function that just returned an int or > something. But then again, I don't really know how to write LLVM IR myself > so I was just going off of what other people told me would be possible. I > could be wrong :) > > > I’m not saying that it is impossible to find such a function, but keep in > mind that even the size of int is baked into the IR. > > -- adrian > > > Maybe not worth worrying about if clang never generates this type of code > anyway, just an idea. > > On Wed, Feb 3, 2016 at 1:35 PM Adrian Prantl <apra...@apple.com> wrote: >> >> For context, here are the relevant LLVM discussions: >> http://reviews.llvm.org/D16569 (D16569: Emit line 0 line information for >> interesting 'orphan’ instructions) >> http://reviews.llvm.org/D9887 [DebugInfo][FastISel] Prevent using debug >> location from previous block for local values >> >> On Feb 3, 2016, at 12:56 PM, Zachary Turner <ztur...@google.com> wrote: >> >> (Also, if clang is not generating code like this currently, maybe it's not >> a priority, but seems worth mentioning the technique anyway, since it could >> have a lot of use for these types of scenarios) >> >> On Wed, Feb 3, 2016 at 12:54 PM Zachary Turner <ztur...@google.com> wrote: >>> >>> I asked around a little bit, and it seems like you do this by >>> hand-writing some LLVM IR (limiting yourself to a subset that is >>> sufficiently platform independent) and having clang link that in alongside a >>> regular executable. Then call your LLVM IR function from C++ and step over >>> it. Would that work? >> >> >> LLVM IR is nowhere near platform independent enough for this to be >> portable. Of course having a test for a single target is probably still >> better than having no test. I’m not sure if the effort of maintaining >> textual IR (which tends to change a lot) in the LLDB testsuite is worth it. >> Another option (not any less messy) would be to compile the test to >> assembler with -S insert a .loc 0 before assembling the file. >> >> -- adrian >> >>> >>> You'd probably need to talk to one of the LLVM guys to figure out how to >>> do that, but it seems like it should work. >>> >>> Assuming it does, this technique would also open the door to writing a >>> lot of test cases that have historically been very difficult to write (such >>> as unwinder tests that need frames to be constructed a specific way, etc). >>> >>> >>> >>> On Tue, Feb 2, 2016 at 5:31 PM Jim Ingham <jing...@apple.com> wrote: >>>> >>>> I don't think Clang does this right now, but Adrian says they are >>>> considering doing it to solve some problems they have with keeping track of >>>> nested inlines. >>>> >>>> Swift does it, but the compiler makes no guarantees as to when this will >>>> happen. It isn't controlled by some pragma, builtin or whatever. So I >>>> know >>>> some places where it will happen today, but there's no guarantee it will >>>> continue to happen in the future. So I'll have to write a test that works >>>> with the current compiler, and fails if the compiler changes so the >>>> relevant >>>> function no longer has line number 0 code right after the prologue. Yuck! >>>> >>>> I don't think it will be any different with clang when/if it starts >>>> doing this. >>>> >>>> Jim >>>> >>>> >>>> > On Feb 2, 2016, at 4:14 PM, Zachary Turner <ztur...@google.com> wrote: >>>> > >>>> > Shouldn't it be possible to force clang to generate code like this? >>>> > If so couldn't you write a test for this by stepping over a function call >>>> > which has this kind of code in it? >>>> > >>>> > On Tue, Feb 2, 2016 at 4:11 PM Jim Ingham via lldb-commits >>>> > <lldb-commits@lists.llvm.org> wrote: >>>> > Author: jingham >>>> > Date: Tue Feb 2 18:07:23 2016 >>>> > New Revision: 259611 >>>> > >>>> > URL: http://llvm.org/viewvc/llvm-project?rev=259611&view=rev >>>> > Log: >>>> > The compiler may use "line number 0" to indicate compiler generated >>>> > goo that it can't >>>> > track a source for. When we are pushing breakpoints and stepping past >>>> > function prologues, >>>> > also push past code from line 0 immediately following the prologue >>>> > end. >>>> > >>>> > <rdar://problem/23730696> >>>> > >>>> > Modified: >>>> > lldb/trunk/include/lldb/Symbol/Function.h >>>> > lldb/trunk/source/Symbol/Function.cpp >>>> > >>>> > Modified: lldb/trunk/include/lldb/Symbol/Function.h >>>> > URL: >>>> > http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Symbol/Function.h?rev=259611&r1=259610&r2=259611&view=diff >>>> > >>>> > ============================================================================== >>>> > --- lldb/trunk/include/lldb/Symbol/Function.h (original) >>>> > +++ lldb/trunk/include/lldb/Symbol/Function.h Tue Feb 2 18:07:23 2016 >>>> > @@ -574,6 +574,14 @@ public: >>>> > CompilerType >>>> > GetCompilerType (); >>>> > >>>> > + >>>> > //------------------------------------------------------------------ >>>> > + /// Get the size of the prologue instructions for this function. >>>> > The "prologue" >>>> > + /// instructions include any instructions given line number 0 >>>> > immediately following >>>> > + /// the prologue end. >>>> > + /// >>>> > + /// @return >>>> > + /// The size of the prologue. >>>> > + >>>> > //------------------------------------------------------------------ >>>> > uint32_t >>>> > GetPrologueByteSize (); >>>> > >>>> > >>>> > Modified: lldb/trunk/source/Symbol/Function.cpp >>>> > URL: >>>> > http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Symbol/Function.cpp?rev=259611&r1=259610&r2=259611&view=diff >>>> > >>>> > ============================================================================== >>>> > --- lldb/trunk/source/Symbol/Function.cpp (original) >>>> > +++ lldb/trunk/source/Symbol/Function.cpp Tue Feb 2 18:07:23 2016 >>>> > @@ -570,6 +570,8 @@ Function::GetPrologueByteSize () >>>> > { >>>> > m_flags.Set(flagsCalculatedPrologueSize); >>>> > LineTable* line_table = m_comp_unit->GetLineTable (); >>>> > + uint32_t prologue_end_line_idx = 0; >>>> > + >>>> > if (line_table) >>>> > { >>>> > LineEntry first_line_entry; >>>> > @@ -578,9 +580,12 @@ Function::GetPrologueByteSize () >>>> > { >>>> > // Make sure the first line entry isn't already the >>>> > end of the prologue >>>> > addr_t prologue_end_file_addr = LLDB_INVALID_ADDRESS; >>>> > + addr_t line_zero_end_file_addr = >>>> > LLDB_INVALID_ADDRESS; >>>> > + >>>> > if (first_line_entry.is_prologue_end) >>>> > { >>>> > prologue_end_file_addr = >>>> > first_line_entry.range.GetBaseAddress().GetFileAddress(); >>>> > + prologue_end_line_idx = first_line_entry_idx; >>>> > } >>>> > else >>>> > { >>>> > @@ -595,6 +600,7 @@ Function::GetPrologueByteSize () >>>> > if (line_entry.is_prologue_end) >>>> > { >>>> > prologue_end_file_addr = >>>> > line_entry.range.GetBaseAddress().GetFileAddress(); >>>> > + prologue_end_line_idx = idx; >>>> > break; >>>> > } >>>> > } >>>> > @@ -607,7 +613,7 @@ Function::GetPrologueByteSize () >>>> > { >>>> > // Check the first few instructions and look for >>>> > one that has >>>> > // a line number that's different than the first >>>> > entry. >>>> > - const uint32_t last_line_entry_idx = >>>> > first_line_entry_idx + 6; >>>> > + uint32_t last_line_entry_idx = >>>> > first_line_entry_idx + 6; >>>> > for (uint32_t idx = first_line_entry_idx + 1; idx >>>> > < last_line_entry_idx; ++idx) >>>> > { >>>> > LineEntry line_entry; >>>> > @@ -616,6 +622,7 @@ Function::GetPrologueByteSize () >>>> > if (line_entry.line != >>>> > first_line_entry.line) >>>> > { >>>> > prologue_end_file_addr = >>>> > line_entry.range.GetBaseAddress().GetFileAddress(); >>>> > + prologue_end_line_idx = idx; >>>> > break; >>>> > } >>>> > } >>>> > @@ -624,10 +631,37 @@ Function::GetPrologueByteSize () >>>> > if (prologue_end_file_addr == >>>> > LLDB_INVALID_ADDRESS) >>>> > { >>>> > prologue_end_file_addr = >>>> > first_line_entry.range.GetBaseAddress().GetFileAddress() + >>>> > first_line_entry.range.GetByteSize(); >>>> > + prologue_end_line_idx = first_line_entry_idx; >>>> > } >>>> > } >>>> > + >>>> > const addr_t func_start_file_addr = >>>> > m_range.GetBaseAddress().GetFileAddress(); >>>> > const addr_t func_end_file_addr = >>>> > func_start_file_addr + m_range.GetByteSize(); >>>> > + >>>> > + // Now calculate the offset to pass the subsequent >>>> > line 0 entries. >>>> > + uint32_t first_non_zero_line = prologue_end_line_idx; >>>> > + while (1) >>>> > + { >>>> > + LineEntry line_entry; >>>> > + if >>>> > (line_table->GetLineEntryAtIndex(first_non_zero_line, line_entry)) >>>> > + { >>>> > + if (line_entry.line != 0) >>>> > + break; >>>> > + } >>>> > + if >>>> > (line_entry.range.GetBaseAddress().GetFileAddress() >= >>>> > func_end_file_addr) >>>> > + break; >>>> > + >>>> > + first_non_zero_line++; >>>> > + } >>>> > + >>>> > + if (first_non_zero_line > prologue_end_line_idx) >>>> > + { >>>> > + LineEntry first_non_zero_entry; >>>> > + if >>>> > (line_table->GetLineEntryAtIndex(first_non_zero_line, >>>> > first_non_zero_entry)) >>>> > + { >>>> > + line_zero_end_file_addr = >>>> > first_non_zero_entry.range.GetBaseAddress().GetFileAddress(); >>>> > + } >>>> > + } >>>> > >>>> > // Verify that this prologue end file address in the >>>> > function's >>>> > // address range just to be sure >>>> > @@ -635,10 +669,16 @@ Function::GetPrologueByteSize () >>>> > { >>>> > m_prologue_byte_size = prologue_end_file_addr - >>>> > func_start_file_addr; >>>> > } >>>> > + >>>> > + if (prologue_end_file_addr < line_zero_end_file_addr >>>> > && line_zero_end_file_addr < func_end_file_addr) >>>> > + { >>>> > + m_prologue_byte_size += line_zero_end_file_addr - >>>> > prologue_end_file_addr; >>>> > + } >>>> > } >>>> > } >>>> > } >>>> > - return m_prologue_byte_size; >>>> > + >>>> > + return m_prologue_byte_size; >>>> > } >>>> > >>>> > lldb::LanguageType >>>> > >>>> > >>>> > _______________________________________________ >>>> > lldb-commits mailing list >>>> > lldb-commits@lists.llvm.org >>>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits >>>> > > > _______________________________________________ > lldb-commits mailing list > lldb-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits > _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
