[lldb][FreeBSD] Add FreeBSD specific AT_HWCAP value

[DavidSpickett]

While adding register fields I realised that the AUXV values for Linux and FreeBSD disagree here.

So I've added a FreeBSD specific HWCAP value that I can use from FreeBSD specific code.

The alternative is translating GetAuxValue calls depending on platform, which requires that we know what we are at all times.

Another way would be to convert the entries' values when we construct the AuxVector but the platform specific call that reads the data just returns a raw array. So adding another layer here is more disruption.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: David Spickett (DavidSpickett)

Changes

While adding register fields I realised that the AUXV values for Linux and FreeBSD disagree here.

So I've added a FreeBSD specific HWCAP2 value that I can use from FreeBSD specific code.

The alternative is translating GetAuxValue calls depending on platform, which requires that we know what we are at all times.

Another way would be to convert the entries' values when we construct the AuxVector but the platform specific call that reads the data just returns a raw array. So adding another layer here is more disruption.

---

Full diff: https://github.com/llvm/llvm-project/pull/84147.diff

1 Files Affected:

• (modified) lldb/source/Plugins/Process/Utility/AuxVector.h (+15-2)

diff --git a/lldb/source/Plugins/Process/Utility/AuxVector.h b/lldb/source/Plugins/Process/Utility/AuxVector.h
index 3b0f55d35e5d11..237c120a426941 100644
--- a/lldb/source/Plugins/Process/Utility/AuxVector.h
+++ b/lldb/source/Plugins/Process/Utility/AuxVector.h
@@ -20,9 +20,13 @@ class AuxVector {
   AuxVector(const lldb_private::DataExtractor &data);
 
   /// Constants describing the type of entry.
-  /// On Linux, running "LD_SHOW_AUXV=1 ./executable" will spew AUX
+  /// On Linux and FreeBSD, running "LD_SHOW_AUXV=1 ./executable" will spew AUX
   /// information. Added AUXV prefix to avoid potential conflicts with system-
-  /// defined macros
+  /// defined macros. For FreeBSD, the numbers can be found in sys/elf_common.h.
+  ///
+  /// Linux and FreeBSD values diverge, so the FreeBSD classes will convert
+  /// some entries to the Linux AT_ value so that LLDB only has to use
+  /// the constants listed here when asking the AuxVector for a value.
   enum EntryType {
     AUXV_AT_NULL = 0,      ///< End of auxv.
     AUXV_AT_IGNORE = 1,    ///< Ignore entry.
@@ -39,6 +43,11 @@ class AuxVector {
     AUXV_AT_EUID = 12,     ///< Effective UID.
     AUXV_AT_GID = 13,      ///< GID.
     AUXV_AT_EGID = 14,     ///< Effective GID.
+
+    // At this point Linux and FreeBSD diverge and many of the following values
+    // are Linux specific. If you use them make sure you are in Linux specific
+    // code or they have the same value on other platforms.
+
     AUXV_AT_CLKTCK = 17,   ///< Clock frequency (e.g. times(2)).
     AUXV_AT_PLATFORM = 15, ///< String identifying platform.
     AUXV_AT_HWCAP =
@@ -60,6 +69,10 @@ class AuxVector {
     AUXV_AT_L1D_CACHESHAPE = 35,
     AUXV_AT_L2_CACHESHAPE = 36,
     AUXV_AT_L3_CACHESHAPE = 37,
+
+    // Platform specific values which may overlap the Linux values.
+
+    AUXV_FREEBSD_AT_HWCAP = 25, ///< FreeBSD specific AT_HWCAP value.
   };
 
   std::optional<uint64_t> GetAuxValue(enum EntryType entry_type) const;

[DavidSpickett]

Some notes:

1. This looks odd in isolation but I need to correct this to enable register fields on FreeBSD, which will be the next PR.
2. clang-format is going to complain about the enum, I will fix push a commit to fix that after this one, so that this commit stays readable.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 982e9022ca4abaad58c693d2b0aba0e908ee2d39 74f9b8cd1fd68298e1b03f749041256639ce1fef -- lldb/source/Plugins/Process/Utility/AuxVector.h

View the diff from clang-format here.

diff --git a/lldb/source/Plugins/Process/Utility/AuxVector.h b/lldb/source/Plugins/Process/Utility/AuxVector.h
index 4175cb73b2..2670b34f6b 100644
--- a/lldb/source/Plugins/Process/Utility/AuxVector.h
+++ b/lldb/source/Plugins/Process/Utility/AuxVector.h
@@ -24,21 +24,21 @@ public:
   /// information. Added AUXV prefix to avoid potential conflicts with system-
   /// defined macros. For FreeBSD, the numbers can be found in sys/elf_common.h.
   enum EntryType {
-    AUXV_AT_NULL = 0,      ///< End of auxv.
-    AUXV_AT_IGNORE = 1,    ///< Ignore entry.
-    AUXV_AT_EXECFD = 2,    ///< File descriptor of program.
-    AUXV_AT_PHDR = 3,      ///< Program headers.
-    AUXV_AT_PHENT = 4,     ///< Size of program header.
-    AUXV_AT_PHNUM = 5,     ///< Number of program headers.
-    AUXV_AT_PAGESZ = 6,    ///< Page size.
-    AUXV_AT_BASE = 7,      ///< Interpreter base address.
-    AUXV_AT_FLAGS = 8,     ///< Flags.
-    AUXV_AT_ENTRY = 9,     ///< Program entry point.
-    AUXV_AT_NOTELF = 10,   ///< Set if program is not an ELF.
-    AUXV_AT_UID = 11,      ///< UID.
-    AUXV_AT_EUID = 12,     ///< Effective UID.
-    AUXV_AT_GID = 13,      ///< GID.
-    AUXV_AT_EGID = 14,     ///< Effective GID.
+    AUXV_AT_NULL = 0,    ///< End of auxv.
+    AUXV_AT_IGNORE = 1,  ///< Ignore entry.
+    AUXV_AT_EXECFD = 2,  ///< File descriptor of program.
+    AUXV_AT_PHDR = 3,    ///< Program headers.
+    AUXV_AT_PHENT = 4,   ///< Size of program header.
+    AUXV_AT_PHNUM = 5,   ///< Number of program headers.
+    AUXV_AT_PAGESZ = 6,  ///< Page size.
+    AUXV_AT_BASE = 7,    ///< Interpreter base address.
+    AUXV_AT_FLAGS = 8,   ///< Flags.
+    AUXV_AT_ENTRY = 9,   ///< Program entry point.
+    AUXV_AT_NOTELF = 10, ///< Set if program is not an ELF.
+    AUXV_AT_UID = 11,    ///< UID.
+    AUXV_AT_EUID = 12,   ///< Effective UID.
+    AUXV_AT_GID = 13,    ///< GID.
+    AUXV_AT_EGID = 14,   ///< Effective GID.
 
     // At this point Linux and FreeBSD diverge and many of the following values
     // are Linux specific. If you use them make sure you are in Linux specific

[DavidSpickett]

And if anyone knows the appropriate way to write this as a doxygen comment, that would be a great help.

[emaste]

(Assuming the comment removal gets squashed into one commit)