<div dir="ltr">(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)</div><br><div class="gmail_quote"><div dir="ltr">On Wed, Feb 3, 2016 at 12:54 PM Zachary Turner <<a href="mailto:zturner@google.com">zturner@google.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">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?<div><br></div><div>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.</div><div><br></div><div>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).</div></div><div dir="ltr"><div><br></div><div><br><br><div class="gmail_quote"><div dir="ltr">On Tue, Feb 2, 2016 at 5:31 PM Jim Ingham <<a href="mailto:jingham@apple.com" target="_blank">jingham@apple.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">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.<br>
<br>
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!<br>
<br>
I don't think it will be any different with clang when/if it starts doing this.<br>
<br>
Jim<br>
<br>
<br>
> On Feb 2, 2016, at 4:14 PM, Zachary Turner <<a href="mailto:zturner@google.com" target="_blank">zturner@google.com</a>> wrote:<br>
><br>
> 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?<br>
><br>
> On Tue, Feb 2, 2016 at 4:11 PM Jim Ingham via lldb-commits <<a href="mailto:lldb-commits@lists.llvm.org" target="_blank">lldb-commits@lists.llvm.org</a>> wrote:<br>
> Author: jingham<br>
> Date: Tue Feb 2 18:07:23 2016<br>
> New Revision: 259611<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=259611&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=259611&view=rev</a><br>
> Log:<br>
> The compiler may use "line number 0" to indicate compiler generated goo that it can't<br>
> track a source for. When we are pushing breakpoints and stepping past function prologues,<br>
> also push past code from line 0 immediately following the prologue end.<br>
><br>
> <rdar://problem/23730696><br>
><br>
> Modified:<br>
> lldb/trunk/include/lldb/Symbol/Function.h<br>
> lldb/trunk/source/Symbol/Function.cpp<br>
><br>
> Modified: lldb/trunk/include/lldb/Symbol/Function.h<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Symbol/Function.h?rev=259611&r1=259610&r2=259611&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Symbol/Function.h?rev=259611&r1=259610&r2=259611&view=diff</a><br>
> ==============================================================================<br>
> --- lldb/trunk/include/lldb/Symbol/Function.h (original)<br>
> +++ lldb/trunk/include/lldb/Symbol/Function.h Tue Feb 2 18:07:23 2016<br>
> @@ -574,6 +574,14 @@ public:<br>
> CompilerType<br>
> GetCompilerType ();<br>
><br>
> + //------------------------------------------------------------------<br>
> + /// Get the size of the prologue instructions for this function. The "prologue"<br>
> + /// instructions include any instructions given line number 0 immediately following<br>
> + /// the prologue end.<br>
> + ///<br>
> + /// @return<br>
> + /// The size of the prologue.<br>
> + //------------------------------------------------------------------<br>
> uint32_t<br>
> GetPrologueByteSize ();<br>
><br>
><br>
> Modified: lldb/trunk/source/Symbol/Function.cpp<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Symbol/Function.cpp?rev=259611&r1=259610&r2=259611&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Symbol/Function.cpp?rev=259611&r1=259610&r2=259611&view=diff</a><br>
> ==============================================================================<br>
> --- lldb/trunk/source/Symbol/Function.cpp (original)<br>
> +++ lldb/trunk/source/Symbol/Function.cpp Tue Feb 2 18:07:23 2016<br>
> @@ -570,6 +570,8 @@ Function::GetPrologueByteSize ()<br>
> {<br>
> m_flags.Set(flagsCalculatedPrologueSize);<br>
> LineTable* line_table = m_comp_unit->GetLineTable ();<br>
> + uint32_t prologue_end_line_idx = 0;<br>
> +<br>
> if (line_table)<br>
> {<br>
> LineEntry first_line_entry;<br>
> @@ -578,9 +580,12 @@ Function::GetPrologueByteSize ()<br>
> {<br>
> // Make sure the first line entry isn't already the end of the prologue<br>
> addr_t prologue_end_file_addr = LLDB_INVALID_ADDRESS;<br>
> + addr_t line_zero_end_file_addr = LLDB_INVALID_ADDRESS;<br>
> +<br>
> if (first_line_entry.is_prologue_end)<br>
> {<br>
> prologue_end_file_addr = first_line_entry.range.GetBaseAddress().GetFileAddress();<br>
> + prologue_end_line_idx = first_line_entry_idx;<br>
> }<br>
> else<br>
> {<br>
> @@ -595,6 +600,7 @@ Function::GetPrologueByteSize ()<br>
> if (line_entry.is_prologue_end)<br>
> {<br>
> prologue_end_file_addr = line_entry.range.GetBaseAddress().GetFileAddress();<br>
> + prologue_end_line_idx = idx;<br>
> break;<br>
> }<br>
> }<br>
> @@ -607,7 +613,7 @@ Function::GetPrologueByteSize ()<br>
> {<br>
> // Check the first few instructions and look for one that has<br>
> // a line number that's different than the first entry.<br>
> - const uint32_t last_line_entry_idx = first_line_entry_idx + 6;<br>
> + uint32_t last_line_entry_idx = first_line_entry_idx + 6;<br>
> for (uint32_t idx = first_line_entry_idx + 1; idx < last_line_entry_idx; ++idx)<br>
> {<br>
> LineEntry line_entry;<br>
> @@ -616,6 +622,7 @@ Function::GetPrologueByteSize ()<br>
> if (line_entry.line != first_line_entry.line)<br>
> {<br>
> prologue_end_file_addr = line_entry.range.GetBaseAddress().GetFileAddress();<br>
> + prologue_end_line_idx = idx;<br>
> break;<br>
> }<br>
> }<br>
> @@ -624,10 +631,37 @@ Function::GetPrologueByteSize ()<br>
> if (prologue_end_file_addr == LLDB_INVALID_ADDRESS)<br>
> {<br>
> prologue_end_file_addr = first_line_entry.range.GetBaseAddress().GetFileAddress() + first_line_entry.range.GetByteSize();<br>
> + prologue_end_line_idx = first_line_entry_idx;<br>
> }<br>
> }<br>
> +<br>
> const addr_t func_start_file_addr = m_range.GetBaseAddress().GetFileAddress();<br>
> const addr_t func_end_file_addr = func_start_file_addr + m_range.GetByteSize();<br>
> +<br>
> + // Now calculate the offset to pass the subsequent line 0 entries.<br>
> + uint32_t first_non_zero_line = prologue_end_line_idx;<br>
> + while (1)<br>
> + {<br>
> + LineEntry line_entry;<br>
> + if (line_table->GetLineEntryAtIndex(first_non_zero_line, line_entry))<br>
> + {<br>
> + if (line_entry.line != 0)<br>
> + break;<br>
> + }<br>
> + if (line_entry.range.GetBaseAddress().GetFileAddress() >= func_end_file_addr)<br>
> + break;<br>
> +<br>
> + first_non_zero_line++;<br>
> + }<br>
> +<br>
> + if (first_non_zero_line > prologue_end_line_idx)<br>
> + {<br>
> + LineEntry first_non_zero_entry;<br>
> + if (line_table->GetLineEntryAtIndex(first_non_zero_line, first_non_zero_entry))<br>
> + {<br>
> + line_zero_end_file_addr = first_non_zero_entry.range.GetBaseAddress().GetFileAddress();<br>
> + }<br>
> + }<br>
><br>
> // Verify that this prologue end file address in the function's<br>
> // address range just to be sure<br>
> @@ -635,10 +669,16 @@ Function::GetPrologueByteSize ()<br>
> {<br>
> m_prologue_byte_size = prologue_end_file_addr - func_start_file_addr;<br>
> }<br>
> +<br>
> + if (prologue_end_file_addr < line_zero_end_file_addr && line_zero_end_file_addr < func_end_file_addr)<br>
> + {<br>
> + m_prologue_byte_size += line_zero_end_file_addr - prologue_end_file_addr;<br>
> + }<br>
> }<br>
> }<br>
> }<br>
> - return m_prologue_byte_size;<br>
> +<br>
> + return m_prologue_byte_size;<br>
> }<br>
><br>
> lldb::LanguageType<br>
><br>
><br>
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<br>
</blockquote></div></div></div></blockquote></div>