We used to jump directly to the program entry point (typically
`_start`), without initializing the program counter. We now initialize
the program counter and the let the program start with the dispatcher,
since it seems a safer solution.
This commit fixes a bug triggered by specifying the `--entry` switch:
the entry point would not be registered as a jump target, instead the
code would try to get the basic block associated to that address,
resulting in an assertion.
The manually specified entry point is now registered as a jump target
coming from global data.
Introduce an option to prevent `revamb` from linking in all the QEMU
helpers. This is useful if the output doesn't need to be compiled, but
just analyzed.
This commit introduces two new passes:
* `GeneratedCodeBasicInfo`: recovers from the IR some basic information
like the size of delay slots in the input architecture, the name of
the program counter and so on. It can also identify the type of a
basic block (e.g., dispatcher, jump target...). *
* `FunctionCallIdentification`: identifies function calls and injects a
marker before the associated terminator instruction.
The idea of these two passes is to try to progressively move information
we used to keep in `JumpTargetManager` into the IR, so that it is more
easily accessible and passes do not need a reference to `JTM`.
In particular by having markers for function calls available during jump
target discovery we don't have to have duplicated and suboptimal
implementation of `isCall`.
This commit also introduce some additional helper functions and an
helper class to quickly.
Every time we don't know where an indirect jump can go, we used to emit
a jump to the dispatcher, however this complicates our analyses, in
particular the computed dominator tree provides less useful information
than it could.
This commit transforms all the jumps to the dispatcher into jumps to a
"anypc" basic block which during analysis just contains an unreachable
instruction, but during finalization this instruction is replaced with a
jump to the dispatcher. A similar (temporary) situation is for the
"unexpectepc" case.
This commit also makes the `visit(Sucessors|Predecessors)` functions
more idiomatic by employing a trait for black lists.
This commit removes all the ELF-specific code from the `CodeGenerator`
class by creating a new class, `BinaryFile` which contains all the
information about the program that might be needed in an image format
independent way. However, `BinaryFile` has some fields which are
specific to ELF, we might want to address this when additional file
formats are supported.
A key benefit of isolating this code is that we can anticipate the
parsing of the input file, so that we have its architecture available
earlier than when `CodeGenerator` is instantiated, therefore we can drop
the `--architecture` parameter.
This commit introduces the usage of symbols, if they are available. We
employ them to produce meaningful names for basic block names.
* Collect the symbols from `.symtab`/`.dynsym`
* Box the `Segments` into a new data structure (`BinaryInfo`) which also
handles symbols.
* `JumpTargetManager::nameForAddress`: produce a meaningful name using
symbols, if possible.
* Spread some `const`-ness
This commit introduces the `noreturn` analysis, whose aim is to detect
all the basic blocks the are doomed to lead to a `noreturn` syscall such
as `execve` or `exit`.
* Implement `NoreturnAnalysis`.
* Include and initialize in the `Architecture` data structure all the
necessary information to detect `noreturn` syscalls. Specifically, the
name of the QEMU helper for syscalls, the name of the register holding
the syscall number and the syscall numbers representing `noreturn`
syscalls.
* `ReachingDefinitionsPass`: make reaching definitions available both in
reaching definitions mode and reached loads mode. This part needs
further cleanup. We also might be willing to implement this with a
`Boost.Bimap`.
* Use `SET` to collect information useful for the
`NoreturnAnalysis`. Also restructure how the `OperationsStack` works
to be more streamlined and keep track of multiple information about
the instruction currently being tracked.
This commit registers for each jump target how we met it, as a flag. It
also keeps track of which pointers in global data have been involved in
materialization performed by SET: those who are not are of special
interest for us, since they are likely function pointers, and are
therefore marked with a specific flag.
Now `CodeGenerator::translate`, `CodeGenerator::translateCall` and
`CodeGenerator::newInstruction` all return
`CodeGenerator::TranslationResult` which covers all the possible results
that the caller needs to handle such abort, stop translation, force a
new basic block or simply proceed.
This patch also prevents reading a PTC temporary that has never been
written (typically due to a mistranslation) by emitting an abort.
* Import OSRA
* Improve the SET (aka `JumpTargetFromConstants`) by introducing the
`OperationsStack` class.
* Review `harvest` logic
* Allow to disable OSRA (along with the sumjump heuristic)
* Take the core of `getNextPC` out of it and move it to `getPC`, a
function returning both the current and the next PC. Also, fix a bug
when reaching the beginning of a basic block.
* Detect "reliable" jump targets: a "reliable" jump target is a jump
target obtained from a store to a PC but it's not a fallthrough jump.
This patch implements `VariableManager::storeToCPUStateOffset` and
`VariableManager::loadFromCPUStateOffset`, which handle in a single
point all the accesses by offset to the CPU state.
* `getTypeAtOffset`: introduce a feature to easily debug how we compute
which field is at a specified offset in the CPU state (`--debug
type-at-offset`).
* Let `getTypeAtOffset` and its wrappers return the offset inside a
field of the CPU state (useful when accessing the third byte of an
integer).
* Use a dedicated class for the `CorrectCPUStateUsage` worklist
If before a call to an heper the PC is saved, it means that the helper
can change the PC, therefore we need to go the dispatcher on return. In
this case, we also have to force the PC after the call to be a jump
target.
When we meet a new PC from the PTC input, find immediately the next PC.
This makes the information available early and removes the necessity for
`closeLastInstruction`.
Give a new, useful, meaning to the `--entry` parameter: it's new purpose
is to be able to easily try to translate the code at a certain address.
In this sense, prevent global data harvesting if `--entry` is specified.
The handling of GVN options has also been improved.
Implement producing a CSV file containing information about the which
PCs have been translated. For each PC it is specified whether its a jump
target or not.
Assigning support variables (such as those for original segments and the
ELF header helper) external linkage and giving them a name prevents the
optimizer from dropping them.
* Create 3 constant global variables (`phdr_address`, `e_phentsize` and
`e_phnum`) in the IR which will be used to populate the auxiliary
vectors at run-time.
* Update compile options for `support.c` to ignore useless warnings and
enable debug information
* Implement in `support.c` some functions required by QEMU run-time and
other cleanups to make it compatible with programs translated from
`_start`, not `root`
* Implement in `support.c` the `prepare_stack` function, which
initializes the base of the stack with environment variables,
arguments and auxiliary vectors
* Improve syscall support
The logic to implement harvesting of new code pointers when we're out of
them during translation, has been moved to `JumpTargetManager`. Its
interface has also been reduced and some logging has been introduced.
At the current stage, if there's nothing to `peek`, we first give a shot
of `SROA` and `TranslateDirectBranchesPass`, and then, if nothing came
out, we go for `EarlyCSE` and `JumpTargetsFromConstantsPass`.
Instead of taking note of the executable ranges exclusively, keep track
of all the segments in `CodeGenerator`. `JumpTargetManager` instead will
keep track of executable areas only.
* Introduce the `SegmentInfo` struct, which simply holds essential
information about the segment such as start and end address,
permissions and a reference to the global variable holding its content.
* Update `CodeGenerator` to keep a vector of `SegmentInfo`.
* `JumpTargetManager`: polish the constructor and make it take the vector
of `SegmentInfo`, from which the executable ranges are then extracted.
Alessandro Di Federico